Disclosed is a reactive power control method for suppressing a transient overvoltage in a DC sending-end power grid of new energy. The method estimates the trend of grid voltage changes by using current and historical signals of the grid voltage, calculates the reactive power command offset value to achieve the effect of reactive power lead control, and combines the optimized reactive power value after lag compensation. The superposition of the lag compensation and the reactive power optimization generates a final command value for a new energy power source, and this command value can ensure that new energy effectively outputs reactive power to participate in the suppression of the transient overvoltage in a DC converter station.