Direct-drive water generation system is connected directly to the water turbine and generator. In order to improve the efficiency and reliability of system, to reduce the inductance of AC side affects the static and dynamic performance of the whole system when the direct-drive water generation system is actively inverting. The paper presents a new design method of the inductance of AC side based on steady-state and transient current tracking, which can meet demands of the direct-drive water generation system, and verifies its feasibility by simulation. At the same time, the parameters designs method of the traditional DC capacitance have some limitations, which does not account for any problems, such as PWM switching cycle of delay caused by the rectifier and inverter DC bus synchronously to feed the problem. In order to resolve such questions, the new design method of the smallest DC capacitor capacity is proposed, and the characteristics of variable flow speed control system was emulated and experimented, the simulation and experimental verification is correct. The results showed that the hydroelectric power converter speed control system not only has the characteristics of two-way flow of energy, but also has power factor controllable network side, the current low harmonic content, the DC bus voltage pump up fast and controllable.