Constant-temperature water jacket is an important part of the lithographic lens working environment controlling system. A small-scale water jacket model is designed to research the key parameters and properties of constant-temperature water jacket. The constant-temperature water controlling system provides deionized water within ±0.001 ℃ to it, and the key parameters of small-scale water jacket is obtained by comparing the variation of three-mirror optical-mechanical system temperature and thermal aberration. The experimental data shows that when the thermal disturbance is introduced and the temperature of the environment is 22.06~22.16 ℃, the temperature of the inside barrel of the three-mirror optical-mechanical system can be controlled within (22±0.01) ℃. The wave aberration is restored to 10.12 nm after thermal aberration, which is almost equal to the status of the assembled and adjusted system. It shows that the structure of the water jacket can satisfy the demand of the temperature controlling for the projection lens. The equal proportion constant-temperature water jacket can be designed based on it.