During the hot functional test of a pressurized water reactor (PWR), passivation operations are conducted in order to reduce the generation of corrosion product source terms after fuel loading. The temperature of the reactor coolant fluctuates during the hot functional test due to various tests and operations. Therefore, the passivation temperature is a key factor affecting the passivation effect of primary circuit structural materials and the duration of the hot functional test. The passivation film has a double-layer structure, with the Cr-rich inner layer providing protection to the metal substrate. Passivation temperature influences the chemical composition of the passivation film. Under the same concentrations of oxidizing-reducing and acidic-basic substances in the reactor coolant, temperature changes may lead to the formation of less stable passivation films. Passivation temperature also affects the growth rate of the passivation film. Within the temperature range of 200 °C to 300 °C, if the same thickness of oxide film is to be formed, a temperature decrease of 20°C may increase the required reaction time by approximately 10 times. Based on experimental research, theoretical analysis, and worldwide operating experiences, the fluctuation of reactor coolant temperature during primary circuit passivation should be minimized, and the maximum deviation from hot shutdown temperature should be less than 20 °C. Suggestions for dealing with temperature anomalies during passivation are also provided.