The hydraulic compensator in marine drilling equipment plays a critical role in regulating the pressure balance between internal and external environments and the machine's oil supply rate. Its working principle involves utilizing seawater pressure to compensate for volumetric changes in hydraulic oil caused by deep-sea pressure and ambient temperature differences, thereby preventing seawater backflow and subsequent equipment corrosion. A mechanical volume analysis on two compensators with different shapes was conducted using Ansys software, and their hydraulic circuits were simulated via AMEsim. Based on the original hydraulic circuit, additional components such as pressure reducing valves, check valves, and overflow valves were incorporated to construct a hydraulic circuit suitable for active operation mode. A comparative analysis of flow velocity before and after the improvements was performed. Furthermore, the influence of different structural parameters on the internal flow field under deep-sea working conditions was investigated. Finally, a new hydraulic compensator was designed accounting for the pressure and temperature conditions of the marine environment. The results demonstrate that the compensator with a multilayer folded structure and an inlet/outlet size of 20 mm delivers optimal performance. Its hydraulic system can supply a larger flow rate within a shorter time and exhibits enhanced adaptive adjustment capability for transient flow variations.