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Centrifugal pump start up process is a complex transient process. Along with the rapid rise of the impeller rotating speed in a short period of time, its characteristic parameters that include head, flow, and shaft power would change rapidly, which may have a very big impact on pump body and system’s secure and stable operation. Therefore, it is very important to do research about the safety and stability of the pump during the startup process. Research of centrifugal pump is mainly concentrated in steady conditions, the application of centrifugal pump is gradually expanding, centrifugal pump will work under unsteady conditions, such as start, stop and other transient conditions, and the working conditions of pump are complicated transient process, which will make a great difference to the safe and stable operation of pump body and the system. Numerical simulation was used to study its transient characteristics during starting period, the computational domain was the entire closed test rig and the model selected was SST-SAS model. During calculating the startup time was controlled by varying the rotational acceleration of the process, then the transient characteristics of pump startup process under different startup time were studied. Combined with the experimental data, it was found that the transient head of the experiment showed good agreement with simulation, and it was also concluded that the peak of the pump head size was little affected by the startup time during the same startup rule of linear type; three-dimensional numerical simulation of the whole circuit was more accurate than the numerical simulation of the local boundary when simulated during the pump startup process; volute pressure pulsation had a great relationship with the pump startup time, and with the decrease of pump startup time, the volute tongue would produce bigger low-frequency pressure-pulse.