This study hopes to:

1. explore whether an increase in the dosage of cognitive flexibility intervention corresponds to greater effectiveness of mindfulness intervention in alleviating emotional distress.
2. explore whether cognitive flexibility mediates the effects of mindfulness intervention on alleviating emotional distress.

Epidemiological findings in "The Lancet Psychiatry" indicated that anxiety disorders, including generalized anxiety disorder, panic disorder, and social anxiety disorder, are the most prevalent category of disorders in China, with a lifetime prevalence of 7.6%. Depression follows closely with a lifetime prevalence of 6.8%. With the outbreak of the COVID-19 pandemic in 2020, the prevalence of both anxiety and depressive disorders increased. However, the current availability of psychological intervention resources in China is inadequate to meet the demand. This underscores the critical importance of developing effective and efficient psychological intervention approaches, as well as investigating their effectiveness and mechanisms to optimize intervention strategies.

Epidemiological findings in "The Lancet Psychiatry" indicated that anxiety disorders, including generalized anxiety disorder, panic disorder, and social anxiety disorder, are the most prevalent category of disorders in China, with a lifetime prevalence of 7.6%. Depression follows closely with a lifetime prevalence of 6.8%. With the outbreak of the COVID-19 pandemic in 2020, the prevalence of both anxiety and depressive disorders increased. However, the current availability of psychological intervention resources in China is inadequate to meet the demand. This underscores the critical importance of developing effective and efficient psychological intervention approaches, as well as investigating their effectiveness and mechanisms to optimize intervention strategies.

In recent years, mindfulness-based interventions (MBIs) have been increasingly applied to alleviate emotional distress in both clinical and non-clinical populations, with their efficacy widely supported. Additionally, numerous researchers have explored the mechanisms underlying mindfulness and MBIs, proposing various theories. One of the mechanisms frequently suggested by researchers is cognitive flexibility. However, there has been limited direct investigation into the mechanisms of cognitive flexibility and its related processes or abilities. Cognitive flexibility (CF) is considered a common etiological factor or transdiagnostic characteristic of emotional distress, including anxiety and depression. Nevertheless, few studies have explored the mechanisms of how mindfulness interventions alleviate emotional distress from the perspective of cognitive flexibility and the transdiagnostic characteristics of anxiety and depression. This lack of research hampers our ability to obtain sufficient information to develop or enhance mindfulness-based intervention methods to assist individuals with emotional disorders or highly emotionally distressed subclinical populations.

This study is grounded in the critical role of CF in the generation and maintenance of emotional distress, as well as the mindfulness principle of approaching pain with awareness and acceptance (non-judgmental and non-reactive). It posits that cognitive flexibility might be a potential mechanism through which mindfulness interventions alleviate emotional distress. Following the criteria for establishing mechanisms, this research investigates this issue. Based on the current state of research, cognitive flexibility as a mechanism for MBIs to alleviate emotional distress meets the plausibility criterion and partially satisfies the strong association criterion and experimental manipulation criterion. However, further research is needed to assess its consistency criterion, temporal precedence criterion, and gradient criterion.

The current study primarily focuses on the experimental manipulation and gradient criteria. The aim is to examine whether the mechanism of cognitive flexibility meets the experimental manipulation and gradient criteria by adjusting the content of the mindfulness intervention for emotional distress (MIED) program, which can directly impact distress tolerance and manipulate the dosage of cognitive flexibility intervention.

Inclusion Criteria:

• - Subjects with scores greater than 21 on the Kessler Psychological Distress Scale.
• - Aged 18-65 years old.

Exclusion Criteria:

• - Subjects who could not access the Internet;
• - Subjects with insufficient Chinese ability;
• - Subjects who have participated in mindfulness based projects for more than 6 weeks before, and / or the current frequency of meditation practice is more than once a week;
• - Subjects with schizophrenia or psychotic affective disorder, current organic mental disorder, substance abuse disorder and generalized developmental disorder;
• - Subjects with high risk of suicide.