In order to objectively reflect the overall development of big data security in China，we adopt the methods of non-dimensionalization and index weight value to conduct a comprehensive assessment for 36 large and medium-sized cities（Excluding Hong Kong，Macao and Taiwan），including municipalities directly under the central government，provincial capitals and cities specifically designated in the state plan，which is based on the indicator system of big data security index. As indicated by the assessment results，cities in the eastern region score higher in general，reflecting a sound momentum. Guiyang and other cities in the western region have emerged to catch up with cities in the east. Meanwhile，cities in the central region enjoy relatively balanced development on the whole. The paper also makes some predictions and suggestions for the development of big data security，in order to provide reference for the local development of big data security nationwide.