Abstract: With the strategic deployment of "Digital China" in the "14th Five-Year Plan", the digital transformation of major cities in China have been developed rapidly. However, assessing the quality of development in the process of digital transformation has become an important issue faced by governments at all levels. The change in electricity demand has long served as the "barometer" and "umbrella" for the operation of China’s economy and society. Starting from electricity big data, this paper focuses on the connotation of digital development in China and constructs a city digital development index system from three dimensions: resource agglomeration, development vitality, and future plasticity. The index is calculated based on data from over 32,000 key enterprises in Shanghai and data on digital infrastructure in Shanghai. The paper also explores the analytical and monitoring capabilities of electricity data in the context of the digital economy.