Gender difference in language use is a hot topic in current sociolinguistic studies. It is of practical significance to explore the gender difference and its causes in code-switching between the standard language and its dialects. This paper, by means of questionnaires and interviews, investigates the frequency of male or female subjects' using the standard language and its dialects as well as their attitudes to them in public places. The researchers find out that the female uses the standard language more frequently than the male, possessing significantly lower degree of agreement to the use of the dialects in public places than the male, and the degree of agreement to the statement from the female "using the standard language or not has no effects on others' opinions of me" is significantly lower than that of the male. Also the paper attempts to discuss the causes of the differences from the perspectives of the society, families and mentality of the people of the two genders.