Abstract: AIM:To evaluate the correlation between coronary artery diameter and slow flow after percutaneous coronary intervention (PCI). METHODS: Quantitative coronary angiography (QCA) and thrombolysis in myocardial infarction frame count (TIMI frame count) were analyzed in 224 target vessels in 192 patients with PCI. The difference of TIMI frame count before and after PCI 2 was defined as “slow flow group,” 3-9 as “normal flow group” and ≥10 as “fast flow group” according to tertile. The 224 target vessels were divided into diameter ≥4 mm group and <4 mm group. Coronary artery lesion characteristics and baseline information were compared among the three groups. Coronary artery lesion characteristics were also compared in vessels of different diameters. Multiple linear regression analysis was performed in coronary artery flow after PCI and its related risk factors. RESULTS: The reference vessel diameters of target vessels were (3.4±0.7) mm, (3.2±0.7) mm and (3.2±0.7) mm (P<0.05). The ratio of big vessels in the three groups were 29% (23/78), 10% (8/80) and 14% (9/66), P<0.01. The plaque areas were (23±11) mm2 and (15±8) mm2 in diameter ≥4 mm group and <4 mm group (P<0.01). The risk factors for coronary artery flow after PCI were age (P<0.05) and reference vessel diameter (P<0.01) in multiple linear regression analysis. CONCLUSION: Slow flow after PCI is related to coronary artery diameter: the bigger the vascular diameter, the higher the risk of slow flow after PCI.