Abstract: In 2021, the scale of flexible employment in China has reached 200 million people, of which self-employment has become one of the main forms of flexible employment. Will the fertility desire of a large number of self-employed employment groups change? Based on the China General Social Survey (CGSS) data in 2013, 2015 and 2017, this paper empirically examines how self-employment affects the fertility desire of second child and its mechanism. It is found that self-employment significantly increases the fertility desire of second child, especially the positive effect of "opportunistic self-employment" on the fertility desire of second child is stronger than "survival self-employment".Heterogeneity analysis shows that self-employment has a greater effect on the fertility desire of second child among women and individuals of eastern region. The results of the mechanism test suggest that self-employment can have a positive effect on the fertility desire of second child by increasing occupational income, subjective well-being, and subjective class mobility expectations. Further research shows that the coverage of basic social security increases the consistency of second-child fertility desires and fertility behaviors among self-employed workers, which is conducive to the conversion of self-employed workers' second-child fertility desires into actual fertility behaviors. This paper provides a useful reference for broadening the research on self-employment and promoting the development of an inclusive social security system covering self-employed employment groups.