Abstract: The hydraulic control rod drive technology (HCRDT) is a newly invented patent and Institute of Nuclear and New Energy Technology of Tsinghua University owns HCRDT’s independent intellectual property rights. The integrated valve which is made up of three direct action solenoid valves is the key part of this technology, so the performance of the solenoid valve directly affects the function of the integrated valve and HCRDT. Based on the conditions occurring in the operation of the control rod hydraulic drive system, the head of the direct action solenoid valve under thermal state was studied by the experiment and analyzed by FLUENT. The results show that the temperature of the coil of the solenoid valve increases with the current firstly. The temperature of the inner wall of the coil is higher than that of the exterior wall, and the temperature of the middle coil is higher than that of the edge of the coil. The performance of the valve in high temperature can be tested by a method. Furthermore, the design of the power of the direct action solenoid valve can be optimized.