Abstract: The coast-down model of the main pump is needed to provide input data for the reactor transient condition design and safety analysis in the preliminary design stage of a nuclear power plant. Existing pump coastdown models almost need the pump design parameters and resistance characteristics of loop system, while the detailed pump structure design is not yet carried out, and resistance characteristics of pipeline are difficult to obtain in the preliminary design stage of power plant. Aiming at the above problems, two pump coastdown characteristic curve calculation models based on the time parameters were proposed. In addition, the coastdown models were verified by the experimental data. The analysis results show that model A agrees well with the experimental data at high speed and deviates greatly at low speed, while model B is close to the experimental data during the whole coastdown process, which can be used for the condition design and safety analysis for nuclear power plant.