Based on the firm-level micro data from China customs and industrial enterprise databases from 2000 to 2007,this paper comprehensively investigates the effects of changes in RMB exchange rates on Chinese manufacturing export firms' markups,and simultaneously reveals possible function mechanisms behind.It comes to the results as follows:firstly,RMB appreciation significantly reduces export firms' markups;and RMB appreciation has stronger negative effects on mark-ups of firms with higher dependence on export;secondly,dynamic analysis shows that the influence of RMB appreciation on export firms' markups may has a delay of one year,which means export firms' markups will decline more as time passes;thirdly,the effects of RMB exchange rates on export firms' markups are significantly featured by heterogeneity:the negative effect of RMB appreciation on export firms' markups decreases with the improvement of firm productivity,and increases with the enhancement of firm financing constraints;in view of firm ownership,markups of private export firms suffer a big hit from RMB appreciation,while processing export firms are less affected as for mode of trade.Furthermore,it explores the role of RMB appreciation in export firms' markups through a mediating effect model,and shows that RMB appreciation reduces export firms' markups through price competition and scale effects.This paper provides some enlightenment and reference for firm behavior choice and trade policy formulation under the condition of the opening-up capital market.