Aim to investigate the relationship between the average platelet volume and severity of coronary atherosclerosis. Methods 1924 adult subjects who underwent coronary angiography were enrolled in the present study. The average platelet volume of the subjects’ was measured by the automate blood analyzer,and the severity of coronary atherosclerosis was defined by the SYNTAX score. Results A significant difference of the level of average platelet volume was found among the different groups（P<0.01）. Spearman correlation analyses indicated that the SYNTAX score was significantly associated with mean platelet volume（r0.687，P<0.001）. Multiple regression analysis suggested that the level of average platelet volume was independently associated with the SYNTAX score. Conclusion The level of average platelet volume was significantly associated with the severity of coronary atherosclerosis.