Abstract: Data flow has dual attributes. It not only creates conditions for the exertion of the key role of data in empowering social development, but also leaves hidden dangers for the spread of data security risks. This is particularly prominent in cross-border data flow. On this basis, the legal governance of cross-border data flows is closely related to the overall national security outlook. How to achieve effective governance of cross-border data flows has become an important issue that China faces in the process of implementing the overall national security outlook. At present, the legal governance of cross-border data flow in China mainly relies on three tools: data security assessment, standard contracts and protection certification. However, the confusing scope of application of data security assessment will limit the governance effectiveness of cross-border data flow. The unclear application relationship among governance tools will easily affect the efficiency of cross-border data flow. The governance rule of discussing each case on a case-by-case basis will increase the cost of cross-border data flow. In light of this, under the guidance of the overall national security outlook, China should, based on the leading position of data sovereignty, the position of the normalization of the free flow of non-core data, and the position of the overall national security bottom line, improve the scope of application of data security assessment, clarify the application relationships among various governance tools, and establish and improve the white list system for the free cross-border flow of data. Realize the optimized governance of cross-border data flow.