Summary Pumps are a type of general machine with many varieties and extensive application. To simulate really the self‐priming process of multistage self‐priming centrifugal pump, the numerical calculation of gas‐water two‐phase flow on a four‐stage self‐priming pump was performed based on ANSYS CFX software. Moreover, a transparent plastic tube was installed at the pump outlet, and the photographic technology was used to observe the appearance of gas‐water escape during the self‐priming process of multistage self‐priming centrifugal pump. The experimental results were compared with the numerical results. It is found that the whole self‐priming process of self‐priming pump can be divided into three stages: the initial self‐priming stage, the middle self‐priming stage, and the final self‐priming stage. Moreover, the self‐priming time of the initial and final self‐priming stages accounts for a small percentage of the whole self‐priming process, while the middle self‐priming stage is the main stage in the self‐priming process, which determines the length of self‐priming time. The experimental results are very close to the numerical results in the initial and middle self‐priming stages. As shown in the following figure, the calculation domain of the multistage self‐priming pump includes inlet section, gas‐water separation cavity, self‐priming cover plate, impeller, pump cavity, diffuser, gas‐water separation cavity, backflow channel, and outlet section. The largest innovation point in this model was the design of a new self‐priming backflow device with high self‐priming performance. Based on a radial diffuser, the device was composed of a gas‐water separation cavity, backflow channel, self‐priming cover plate, and gas‐water mixture cavity.