[Purpose/significance] As the volume of government big data increases, insufficient data governance is a prominent problem in realizing its value. Research on government big data governance system and practice is crucial to improve the level and efficiency of big data application and promote the development of social intelligence. [Method/process] Based on the research results of big data governance at home and abroad, a government big data governance system is constructed, which consists of three key domains: organizational structure, rules and standards, and technical support. With the help of Nvivo 11 Plus qualitative analysis tool, 43 policy texts related to big data governance in Shanghai, Beijing and Shenzhen are encoded and mapped with the constituent elements of the governance system. [Result/conclusion] The coding results support and explain the key domains of the government big data governance system and its constituent elements. At the same time, although the key domains of the government big data governance system are the same, from the policy level, the government big data governance practice has different emphases and targeted characteristics, which has certain reference significance for guiding our government big data governance.