Aim To explore the predictive value of serum free triiodothyronine (FT3) on the long-term prognosis of patients with coronary heart disease after percutaneous coronary intervention (PCI). Methods All the subjects were from a prospective cohort study (PRACTICE study). In this study, 15 250 patients with coronary heart disease after PCI in the First Affiliated Hospital of Xinjiang Medical University were selected, and the clinical data, FT3 and creatinine were collected. All the subjects were followed up regularly, and the primary follow-up endpoints were all-cause mortality and cardiogenic mortality, the secondary endpoints were major adverse cardiovascular events (MACE) and major adverse cardiovascular and cerebrovascular events (MACCE). According to the admission criteria, 3 109 patients were finally included in this study. According to the baseline value of FT3, patients were divided into normal FT3 group (FT3:3.65～6.8 pmol/L, 1 446 cases) and low FT3 group (FT3＜3.65 pmol/L, 1 663 cases). Kaplan-Meier analysis was used for survival analysis, and Log-rank test was used for survival comparison. Multivariate Cox regression analysis was used to evaluate the risk factors of the follow-up results of the two groups. Results Compared with the normal FT3 group, all-cause mortality and cardiogenic mortality in the low FT3 group increased significantly (P＜0.05). Kaplan-Meier analysis showed that the cumulative risk of all-cause mortality and cardiogenic mortality increased in the low FT3 group (P＜0.05).Multivariate Cox regression analysis indicated that the risk of all-cause mortality increased by 1.639 folds in the low FT3 group (HR＝2.9,5%CI:1.385～5.348, P＝0.007), while no statistical difference was found in cardiogenic mortality after adjusting for multiple factors (P＝0.125). Conclusion The decrease in serum FT3 levels has important predictive value for all-cause mortality after PCI in patients with coronary heart disease.