The invention provides a dynamic reactive power reserve optimization method for improving transient voltage stability of an alternating-current and direct-current power grid. The method comprises the steps of determining a key fault set and a key node set which influence the transient voltage stability of a power system, and sequentially ranking nodes; adjusting reactive power output of dynamic reactive power compensation equipment and calculating the trajectory sensitivity of the dynamic reactive power compensation equipment; ranking m dynamic reactive power compensation equipment and calculating the weight coefficients of the nodes in the dynamic reactive power compensation equipment; calculating the capacities of the dynamic reactive power compensation equipment, establishing a dynamic reactive power reserve optimization model and solving the dynamic reactive power reserve optimization model. The dynamic reactive power reserve optimization method for improving the transient voltage stability of the alternating-current and direct-current power grid provides auxiliary decision-making support for improving the transient voltage stability of the multi-direct-current-drop-point power grid, and has great importance in improving the allowance of the transient voltage stability of the large-scale alternating-current and direct-current power grid, establishing a smooth power transmission passage between a transmitting end and a receiving end, improving the transmission capacity of the alternating-current and direct-current power transmission passage and improving the operation economy and the power quality of the power grid.