Chronic myeloid leukemia (CML) is a malignant disease of acquired hematopoietic stem cells. The BCR-ABL fusion gene is the pathogenic basis of CML. Tyrosine kinase inhibitors (TKIs) are targeted drugs for this fusion protein. With the wide clinical application of TKIs, the efficacy of CML patients has been greatly improved. However, there are still a significant number of patients who have poor response to the first generation of TKI drugs, imatinib, most of them have early molecular response failures (BCR-ABL（IS）>10% at 3 or 6 months) ，which means lower rates of molecular response, increased risk of progression, and higher overall survival. For them, the early conversion of dasatinib might be a better choice.

Inclusion Criteria:

1.18-65 years old； 2.CML-CP,and Imatinib treatment longest for 6 months ； 3.Q-pcr monitoring of BCR/ABLIS failed to achieve the best therapeutic effect（BCR/ABLIS>10.00% in 3m or BCR/ABLIS>1.00% in 6m）； 4.No previous history of malignant tumor; 5.Informed consent of the patient or his legal representative

Exclusion Criteria:

1. History of CML-CP or CML-AP;
2. Resistant to dasatinib,or treatment with imatinib more than 6 months;
3. Received allogeneic hematopoietic stem cell transplantation,or immunotherapy;
4. woman who is pregnant or nursing
5. Combined with other serious organic diseases, serious arrhythmia, pulmonary hypertension, cardiomyopathy, serious autoimmune diseases.

CML-CP patients treated with imatinib failed to achieve the best therapeutic effect（BCR/ABLIS>10.00% in 3m or BCR/ABLIS>1.00% in 6m）convert to dasatinib.