Abstract: The natural circulation test of CAP1400 passive residual heat removal heat exchanger system（PRHR）is one of the first plant only tests and the major plant transient tests during the commissioning. During the natural circulation test, the temperature, pressure, liquid level and other parameters of the reactor primary circuit change dramatically, which increase the test risk and propose higher requirements for the operation control of the unit. Based on the AP1000 commissioning test practice, it is proposed to perform the PRHR natural circulation test using real decay heat generated following the reactor operation from the perspective of reducing test risk. At the same time, it analyzes the safety risks caused by the drastic changes in the parameters of the primary loop pressure, temperature, pressurizer level and the external source range detectors of the reactor during the test, and formulates corresponding countermeasures to provide the strong support for the safety implementation of subsequent CAP1400 PRHR natural tests.