The basic principle of measuring water level of high-pressure(HP) heater and the method for finding measurment deviation of different instruments are introduced in 1 000 MW units of Huaneng Yuhuan Power Plant.The reasons of why the measurement deviation occuring of the magnetic-flap and pressure-difference water-level meter are analyzed.Furthermore,the problems of water-level measurement existed in barrel,installation and maintainance are pointed out.A new method for assistant determination of water-level measuring locations is presented,where the temperature gradient of barrel surface is measured by infrared thermometer and thermal mapper.The suggestions for treating measured deviation of the water level are discussed,providing references to the installation,trouble shooting,operation and maintenance of water-level measurement of HP heater in power plants.