Abstract: In the research and calculation of energy storage capacity both domestically and internationally,statistical methods are generally used to solve the problem, selecting the most economically optimal solution in the long run from a probabilistic perspective. However, this approach does not consider the characteristics of electrical components and lacks specificity. Alternatively, software solutions are used to better evaluate the electrical characteristics of components, but due to the inadequacies of the software itself, there are deficiencies in energy storage optimization. The overall process is overly complex. Based on engineering practice, this paper focuses on the diverse demands of microgrid for energy storage technology. Combining the advantages of statistics and software, it emphasizes simplifying complex problems from the perspective of engineering practice. The main innovation lies in: targeting the main technical characteristics of energy storage batteries, loads, and power supplies in off-grid microgrid systems, combining actual project data from microgrid, decomposing the composite factors affecting energy storage charging and discharging, load fluctuations, and power supply from sources such as wind and solar, conducting source-load-storage power curve matching analysis, and deriving a calculation method for the energy storage capacity of off-grid microgrid based on source-load-storage balance. This method can effectively ensure the safety and stability of microgrid, improve power supply efficiency and reliability, and facilitate the healthy development of smart microgrid.