Ethnic attitudes is an important component of ethnic identity, also is an important variable which used to measure ethnic relations, a strong in-group favoritism easily lead to negative emotion, hostility and discrimination behavior toward out-group, and even induce violation and conflict between ethnic groups. Early childhood is an important period for the formation and development of ethnic attitudes, foreign studies found that there is an important relationship between the psychological adjustment and positive attitude or ethnic identity for ethnic minority children. But current studies on the development of ethnic identity almost from western countries, few studies have examined the Chinese minority children. China is a unified multi-ethnic country, and there are differences in western countries in the social context, ethnic policy and residential patterns etc., these factors likely to affect the formation and development of ethnic favoritism attitude. The present study attempted to extend research object to preschool children from the perspective of developmental psychology, discussed on the formation of children's mental age stage when children form ethnic favoritism attitude, explored the development and change tendency of implicit and explicit ethnic attitude. We selected children from Hui ethnic group as the participants of the present study, through two studies, explored two questions respectively: The first question is when does children form in-group favoritism attitude, do they prefer in-group or out-group? The second question is how does children’s ethnic attitude change with the growth of age? Study 1 selected 3, 4, 5 and 6 years old children as participants, used preschool racial attitude measure(PRAM), we tested children’s in-group and out-group favoritism attitude; Study 2 selected 6, 10 and youth adult as participants, used the implicit association test(IAT) and self-report method, measured participants’ implicit and explicit favoritism attitude toward in-group and out-group. The result of study 1 showed that: 3 years old children did not show significant difference on the evaluation of the in-group and out-group, but there were significant differences for 4, 5 and 6 years old children, they gave more positive traits toward the in-group compared with the out-group, this means that the children had been formed in-group favoritism attitude at the age of 4; the result of study 2 showed: with the growth of age, there was a sustainable growth for children's implicit in-group favoritism attitude; though the explicit attitude remained stable, still exhibited in-group favoritism. The present study suggested that preschool children as early as 4 years old had formed the ethnic attitude, the results were basically consistent with the foreign research results. But in our study, we found no out-group favoritism phenomenon for Hui ethnic group children (though they are ethnic minorities), this was mainly attributed to the difference of the social context between China and some western countries(such as America), because China has no serious racial discrimination history compare to western countries, ethnic status relatively equal. In addition, ethnic favoritism attitude is established in a comparative process, attitude of reference group toward in-group also affected the ethnic favoritism attitude. Future research should pay more attention to the social environment, family and peer effects of various factors on the development of children's ethnic group favoritism attitude.