Abstract: The controllable current source converter (CSC) is considered to be an important research point of high voltage direct current (HVDC) technology. The development of reverse blocking integrated gate commutation thyristor (IGCT) promotes CSC application feasibly. However, due to its current source characteristics, most of the researches mainly adopt the constant DC current strategy, while the research on power control strategy under constant DC voltage is less, seriously restricting its engineering development. In this paper, the mathematical model of CSC is established, and the influence variables of active and reactive power are obtained. Then, the d-q axis component of the capacitor voltage is decoupled, and the inner loop and outer loop control strategies are proposed. After that, the power operation range of the CSC is analyzed with the constraints of DC voltage and modulation ratio. Finally, a hybrid transmission system based on conventional LCC and CSC is built, and the proposed control strategy is analyzed. The research indicates that the proposed power control strategy can decouple active power and reactive power, as well as obtain excellent power regulation effectiveness.