Abstract: Pressurizer is the main equipment of the pressure safety system of PWR nuclear power plants. Its water level reflects the water volume of the primary loop, which is one of the key parameters for the operation and control of the pressurizer. Based on the two-zone unbalanced model, this paper simulates the water level change under the condition of steam leakage and tests the characteristics of water level measurement for the steam leakage condition of the pressurizer, and the pressure drop of the water level under the pressure drop rate of 2.6~7.8 kPa/s in the pressurizer was investigated. It is found that the water level calculated by the pressure difference correction liquid zone density has a good follow-ability in the case of pressure transient, which can better reflect the water level characteristics. Pressure drop characterizing the change of the density in the liquid region of the pressurizer during the pressure reduction, the transition time is less than 40s and there is no strong correlation between the transition time and the single factor of the pressure drop rate. This provides basic research data for the safe operation of the pressurizer.