Objective To analyze the association between PM2.5 exposure in early and middle pregnancy and the cognitive-motor development of their offspring,and provide evidence for air pollution protection during pregnancy. Methods Totally 190 pregnant women who built cards and labored in Shanghai First Maternal and Infant Hospital during June 2014 and April 2015 were selected.Questionnaires were filled when they built cards in our hospital,which got the information of residential address,type of housing and floor distribution.The penetration model was used to transform outdoor atmospheric PM2.5 concentration into indoor PM2.5 exposure concentration as PM2.5 exposure level during pregnancy.The cognitive-motor development assessment of infants was conducted during the "42 day physical examination after postpartum" using "Ages and Stages Questionnaires-Third edition,ASQ-3".Two independent sample t-test and multi factor linear regression analysis were used to analyze the correlation between PM2.5 exposure and the cognition-motor development of their offspring. Results During the first trimester of pregnancy,scores of gross motor and fine motor of infants in normal exposure group were higher than those in exceeded exposure group,as well as the total ASQ-3 score.The differences were statistically significant (P<0.05).PM2.5 exposure level during the first trimester of pregnancy increased each one unit,the scores of each aspect in ASQ-3 decreased 0.53~0.62 points,the total score of ASQ-3 decreased by 2.0 points.In the second trimester,the PM2.5 exposure's effect was different.Although the PM2.5 exposure's level in the second trimester of pregnancy also showed a tendency of decreasing the ASQ-3 score,however,the difference was not statistically significant (P>0.05). Conclusions Compared with PM2.5 exposure in the second trimester of pregnancy,the PM2.5 exposure during the first trimester of pregnancy makes a more serious impact on the cognition-motor development of their offspring.So the protection for atmospheric pollution should focus on the early stages of pregnancy.