<p>Subsea Christmas tree tubing hanger running tools play a critical role in offshore oil production, and their hydraulic transmission systems directly influence the efficiency and safety of well completion operations. This study uses Advanced Modeling Environment for performing Simulation of engineering systems (AMESim) to model and simulate the hydraulic transmission system of a subsea Christmas tree tubing hanger running tool in the Liuhua 11-1 oilfield in the South China Sea. A distributed parameter model is employed to capture the dynamic characteristics of long umbilical pipelines. A multi-parameter co-optimization framework is introduced to address the limitations of single-variable optimization. The analysis systematically examines how four variables — umbilical length, diameter, pump displacement, and accumulator capacity — jointly affect dynamic response, pressure fluctuations, and stability. Simulationbased optimization reduced actuation time from 30-34 seconds to 3-8 seconds for umbilical lengths of 900-1000 meters and pipe diameters of 3/4, 1/2, or 3/8 inch, thereby significantly improving the system’s response speed. By increasing pump displacement to exceed 2.5 cm³·rev^–1, the minimum transient pressure was maintained above 25 MPa, which reduced pressure variation and enhanced system stability. The proposed optimization provides a practical reference for the design of subsea Christmas tree tubing hanger running tools in deepwater oil and gas operations.</p>