Abstract: Hydraulic control rod drive technology (HCRDT) is a newly invented patent owned by Institute of Nuclear and New Energy Technology of Tsinghua University with independent intellectual property rights. Hydraulic cylinder is the core part of this technology, so the sealing performance of hydraulic cylinder directly affects the performance of the HCRDT. A new experiment table was designed and used to test the seal of hydraulic cylinder to get leakage at various pressures and starting pressure at normal temperature. The result shows that the sealing performance of the hydraulic cylinder with three sealing rings is good enough for HCRDT. The leakage of the hydraulic cylinder at constant pressure is stable, and the leakage increases linearly with pressure lifting. The results provide the experimental data for the model of HCRDT moving. Furthermore, the design of HCRDT can be optimized.