Abstract: In order to get the maximum speed setting standard during the temperature-rise period of CAP1400 reactor coolant pump which rated speed was 1500 rpm, the third similarity law and dimensional analysis were used to derive the setting formula of rotation speed which guaranteed that the axial force and power did not exceed the value of normal operating point. The maximum speed of AP1000 and CAP1400 were obtained according the parameters of the normal operating point, and the calculated value of AP1000 was 87.5% rated speed, which was corresponded to the current maximum speed setting of AP1000. The validated numerical computation of the self-designed RCP hydraulic model was carried out to verify the axial and radial force in different settings. The results show that the relation of axial force conforms to the theory when the maximum speed was set to ensure the safety of the axial force. The setting formula of the rotation speed which guaranteed both axial force and power can be used to set the maximum speed during startup process of CAP1400 reactor coolant pump.