Based on the introduction of the heterogeneous enterprise model of export product quality and its appropriate expansion,the paper explains how the dual circulation affects export product quality from the theory of the dual dimensions of"quantity"and"smoothness".The study shows that,firstly,domestic and international circulations and their interaction can significantly promote the upgrading of export product quality.Second,there are significant differences in the effects of the domestic and international circulations on the export product quality for different regions and different export destination countries.Third,the upgrading effect of the dual circulation on export product quality is a single-threshold effect,and the elasticity coefficient of the upgrading of export product quality is higher as the level of mutual promotion of the dual circulation increases.Fourth,the poor economic circulation not only affects the promotion effect of the domestic circulation on export product quality upgrading,but also hinders export product quality upgrading through the international circulation.The findings of the study have important policy implications for reshaping the new competitive advantages of exports from the dual dimensions of"quantity"and"smoothness"by truly giving full play to the"dual circulation"development pattern.