In order to solve DC voltage control problem of two-terminal VSC-HVDC system without communication, on the basis of detailed analysis of existing control modes, an improved DC voltage margin control strategy is proposed in this paper. The proposed controller realizes the exchange of different control modes before PI controller by constructing an error function and weigh coefficient of quadratic function. Compared with traditional DC voltage margin control priciple, the proposed strategy can simplify the controller structure, and meanwhile it can greatly reduce the limit level of DC voltage during fault-ride-through and power reversal. Simulation results prove the effectiveness of the proposed method.