This paper discusses low speed double stator permanent magnet generator design combined with control strategies. The study is based on analytical model. The results indicate that generator structure design is a compromise between torque volume density, power efficiency and control strategy. The reactance value presents an important factor for the system power efficiency and selection of control strategy. The work will focus on the tidal speed below its rated value. The rotational speed of turbine is proportional with tidal speed to maximize the power coefficient. For the same rotational speed, the generator power loss is different when it is controlled by different control strategy. An optimal control strategy can be chosen for special turbine rotational speed or tidal current speed.