The study is to further exploring the optimal switching strategy by evaluating the pharmacodynamic responses as well as adverse events in patients with complexity of coronary artery disease managed by percutaneous coronary intervention (PCI). All participants will be divided into three groups and recieving ticagrelor 90mg plus aspirin 100mg at 12 hours after the last dose of clopidogrel; recieving ticagrelor 90mg plus aspirin 100mg at 24 hours after the last dose of clopidogrel; recieving ticagrelor 180mg plus aspirin 100mg at 24 hours after the last dose of clopidogrel.

Inclusion Criteria:

1. Age between 18-75
2. Patients with complexity of CAD determined by coronary angiography and implanted stent successfully
3. Taking clopidogrel 75mg daily over 5 days or paients never took clopidogrel previously should receive 300-600mg drugs at least 12 hours before coronary angiography
4. Agreeing to participate in this trial and signed the written informed consent.

Exclusion Criteria:

1. They contraindicated with ticagrelor (including: allergying to ticagrelor or its active metabolite
2. Concomitanting therapy with a strong cytochrome P-450 3A inhibitor or inducer
3. Previous intracranial haemorrhage or ongoing bleeds
4. Moderate or severe hepatic impairment)
5. Having a previous medication with ticagrelor or long term anticoagulation
6. Having a history of asthma or chronic obstructive pulmonary disease (COPD) and recurrent attacked
7. Having an uncontrolled hypertension>180/110mmHg
8. Having a hemoglobin<100g/L 9.Having a platelet counts<100×10^9/L
9. Having severe renal impairment (clearance<30mL/min)
10. Having a history of hepaein-induced thrombocytopenia (HIT)
11. Having a pregnancy or were during lactation.