The present study aimed to explore the relationship among the psychological distance between different ethnic groups，difference of the social classes and stereotype，and examines the mediating effect of psychological essentialism of ethnicity between stereotype and cultural attachment. A sample of 303 Mongolian college students was recruited in the study to complete ethnic distance，social classes，stereotype，psychological essentialism of ethnicity and cultural attachment questionnaire. The results indicated that：（1）the felling of the ethnic distance，difference of the social classes influenced the stereotype；（2）there was the mediating effect of psychological essentialism of ethnicity between stereotype and cultural attachment. Practical implications of these results imply that controlling out-group perception and holding more social constructivist belief can be used as the vehicle for improving ethno-national relations and cross-cultural adjustment.