Energy-saving diagnosis and energy audit is an important foundation for the promotion of energy saving and implementation of the "Green Action". However, currently energy-saving diagnosis and energy audit are only accomplished by specialized qualified energy-saving service units, which relies on manual site detection that costs a large number of time and effort, while it is very inefficient and to the disadvantage of the work of energy audit. Therefore, to develop an easily-use tool for energy-saving diagnosis and energy audit is of great significance of the improvement of both efficiency of energy audit and initiative of the users to join the work of energy audit. The article describes the new APP for energy saving analysis work, the APP is developed based on Android, which is called electrical energy-saving calculator. In this paper, the APP function is introduced in details, it mainly including transformer energy-saving module, motor energy-saving module and lighting device energy-saving module. Then the theory and calculation method of energy saving is described. Finally, an example is given to verify the APP's rationality and practicability. Taking use of this APP, the electricity users especially dedicated users will be able to make energy-saving and diagnosis work, and increase the efficiency of energy-saving diagnosis. Its convenient operation help the enterprises maximize energy saving production.