To reduce the risk of transient voltage instability caused by the dynamic load of the system, especially the increase of the proportion of the motor load, a dynamic reactive power optimal configuration method is proposed. In order to obtain the smallest risk of transient voltage instability and the smallest dynamic reactive compensation cost, the algorithm takes the dynamic reactive compensation device capacity and installation position into overall plan and consideration. The critical fault set and the candidate buses of dynamic reactive power compensation are determined by the transient voltage instability risk index and sensitivity index. The capacity of each dynamic reactive power compensation device as variables into the fireworks optimization algorithm to solve. A spark screening link is added in the optimization algorithm for reducing the optimization process time. The simulation results of IEEE39-bus system show that the proposed method can better reduce the transient voltage instability risk under the same reactive power compensation cost compared with the optimization method only considering the dynamic reactive power compensation device installation position. This work is supported by National Natural Science Foundation of China (No. 51507116).