According to previous studies of theory of mind (ToM), social environment and cultural background affect individuals' cognitive ability to understand other people's minds. There are cross-group differences in ToM. The present study aimed to examine whether social environment and culture affect the ToM in Uygur and Han groups and whether the individual's cognitive ToM and affective ToM show in-group advantages. Han and Uygur college students were recruited as participants. The "self/other differentiation task" was used to measure cognitive ToM (Study 1), and the "Yoni task" was used to measure both cognitive and affective ToM (Study 2). We found that Han participants processed the cognitive and affective states of others faster and more accurately than Uygur ones. Uygur and Han participants processed in-group members' cognitive and affective states faster and more accurately. Furthermore, Uygur participants were more accurate in the cognitive ToM processing of in-group members, while Han participants were faster in the affective ToM processing of in-group members. The findings indicated that ethnic culture and group identify might influence ToM processing. Strengthening exchanges between ethnic groups may enable individuals to better process out-group members' psychological states.