Abstract: After our country proposed the three-child policy, governments at all levels have successively introduced a number of favorable fertility policies, but people’s fertility intentions are still low, and the birth rate is not optimistic. This article takes 121 individual cases as the survey subjects and uses qualitative comparative analysis methods to explore the combined effects of multiple factors on the willingness to have a third child, as well as the interactive relationships between different factors. Research has shown that there are no necessary conditions for a single factor to constitute fertility intention, but there are different combinations of conditions that lead to higher fertility intention. Specifically, it can be summarized as follows: high-income rural or urban couples of childbearing age who have relatives to take care of their children, or high-income rural residents who have a certain herd mentality under the influence of national fertility policies, have a stronger willingness to have three children. It is suggested that the government should reduce the economic cost of childcare, improve the maternity leave system, implement flexible working hours for women of childbearing age, improve the efficiency of childcare services, increase publicity, change people’s childbearing concepts, and take differentiated policies and measures for different childbearing subjects.