The invention relates to a dynamic test method of a vehicle fuel cell engine in a power assembly loop. The method comprises the following steps: S1) establishing a power system model for a vehicle; S2) serving a working condition sequence as input of the model; S3) enabling a real-time computer to be in data communication connection with a fuel cell engine, an electronic load and a data acquisition system, and enabling the electronic load and the data acquisition system to be connected with the fuel cell engine; S4) arranging the model and the working condition sequence in the real-time computer; S5) loading the working condition sequence, operating the model in the real-time computer and finishing working condition circulation; and S6) according to the collected data, estimating dynamic performance of the fuel cell engine. Compared with the prior art, by loading the overall power system model to a test platform, and through connection between a sensor and the electronic load, a closedloop is formed with a measured object fuel cell engine system object, and the purpose of obtaining the performance of the fuel cell engine in road test on the test stand can be realized.