This is a randomized, double-blind, multicentral clinical trial to investigate the efficacy and safety of Fengshigutong Capsule in the treatment of active ankylosing spondylitis(AS). The primary purpose is to assess the different maintaining treatment programme in AS patients with controlled inflammation by Imrecoxib. The trial will include 180 patients who will be divided into three group: Fengshigutong Capsule plus Imrecoxib group, Imrecoxib group and Fengshigutong Capsule group. Patients will complete the 4-week therapy.

Inclusion Criteria:

• 18 to 65 years
• Meet 1984 modified New York criteria for AS
• The Bath AS Disease Activity Index (BASDAI) ≥4 on a 0-10-cm visual analog scale or the Ankylosing Spondylitis Disease Activity Score using the C-reactive protein level (ASDAS-CRP) ≥1.3
• NSAIDs washout period of at least 7 days prior to randomization
• DMARDs washout period of at least 4 weeks prior to randomization
• Corticosteroids washout period of at least 2 weeks prior to randomization
• Biological agents washout period of at least 3 months prior to randomization.

Exclusion Criteria:

• Peptic ulcer
• Unstable cardiac diseases
• Hematologic disorders
• Psychosis
• Malignancy
• Multiple sclerosis
• severe COPD
• fibromyalgia and other rheumatic disease
• Corticosteroids were injected into the articular cavity within 3 months
• Chinese medicine was taken within 28 days
• Pregnant and lactating women
• Alcohol and drug abuse
• Spinal cord compression