This is a prospective single center, randomized controlled clinical study aimed to compare the clinical and angiographic follow-up results of patients with in-stent restenosis(ISR) after coronary drug eluting stent(DES) implantation treated by fractional flow reserve -guided and angiography guided drug eluting balloon(DEB) intervention. This study intends to confirm the clinical benefits of optimizing DEB intervention of DES-ISR by FFR.

420 patients with DES-ISR will be recruited in this study. After angiography, patients with DES-ISR to be treated with DEB will be randomly assigned to FFR-guided and angiography-guided groups. In FFR group, FFR at maximum hyperemia will be measured after pretreatment of DES-ISR lesion by balloons(non-compliant balloon, cutting balloon or scoring balloon). If FFR <0.9, the operator will dilate the DES-ISR lesion again before another FFR is measured. If FFR>=0.9, DEB will be used and final FFR will be measured at the end of the procedure. In angiography group, the operator will treat the DES-ISR lesion with balloons(non-compliant balloon, cutting balloon or scoring balloon), and then DEB without FFR guidance.

Inclusion Criteria:

In-stent restenosis(ISR) occurred more than 6 months after drug eluting stent (DES) implantation

Exclusion Criteria:

1. ISR in bare metal stents and biodegradable stents
2. Complicated with immune diseases
3. ISR in left main DES
4. Suffer from renal failure requiring dialysis treatment or is undergoing dialysis treatment
5. Severe cardiac insufficiency (LVEF <30%)
6. Subjects with ST segment elevation myocardial infarction within 7 days of onset of chest pain
7. Pregnant or lactating women
8. Combined with other diseases, life expectancy <1 year
9. Follow - up visits required by the protocol cannot be followed, or the investigators believe that the participation of subjects in the trial will increase the risk

patients with coronary artery disease and DES implantation.