The quasi-synchronous compensator is a type of synchronous generator, which can work in a low loading factor and provide reactive power support to power system. For the enhancement of transient voltage stability, this paper proposes an optimal dispatch method by regulating those quasi-synchronous compensators. At first, a supporting ability index is defined for each generator based on trajectory sensitivity. Then an optimization model is established under the constraints of various operating conditions. At last, the optimal terminal voltage scheme is obtained through the solution of the proposed model. The simulation results suggest that, the proper dispatch of the quasi-synchronous compensator is able to regulate the transient voltage of unstable faults into stable ones.