Hybrid systems that integrate wave energy converters (WECs) with floating offshore wind turbines (FOWTs) are considered to be key equipment to deeply exploit marine renewable energy. The power take-off (PTO) system is an important component of the hybrid system, whose parameters also have a significant impact on the hybrid system’s performance. In this paper, a wind-wave hybrid system using hydraulic PTO systems is proposed. A numerical simulation framework based on the linear wave theory and basic equations of hydraulic components is built and verified. The influence of six critical hydraulic parameters on the wave energy capture and motion response performance of the hybrid system is investigated. Specifically, the parameters of piston area, motor displacement, and equivalent generator damping affect the performance of the hybrid system similar to changing the damping term of the PTO system. The parameters of the initial gas volume and the pre-charged pressure of the accumulator affect the wave power capture only for short wave periods, while the motion response of the hybrid system increases with the increase of these two parameters. The parameter of orifice area of the throttle valve affects the performance of the hybrid system slightly only when it is small. The optimal value of partial hydraulic parameters and their corresponding peak performance are also discussed.