Meeting the needs of care services for children under 3 years old has become a livelihood project. From the multi - source theory perspective，this paper analyzed the problem flow，policy flow and political flow. The article finds that the opening conditions of the policy window of child care service for children under the age of 3 included：the urgent problem flow has been met；the government’s philosophy of “the young nurtured”；and the political flow supported by the national sentiment has been put on the agenda. What has not yet been achieved is that the policy plan lacks maturity. Through the analysis of the relevant policy document，we found that the following problems in the current implementation scheme: the policy protection mechanism is not yet perfect，the government’s publicity is insufficient，and the service content is limited. To open the“policy window”，the paper suggests strengthening the core concept of government， promoting multi-party participation，and improving the policy guarantee.