There is a problem that conventional excitation control fails to make full use of the synchronous condenser transient nonfunction during the fault period. Also it is difficult to accurately and effectively support the voltage of the power network. Thus a staged excitation control optimization strategy considering the saturation parameters of the transformer is proposed. First, the expression of the transient reactive power output of the phase modulator is deduced, and the influence of saturation parameters and different operating conditions on the transient reactive power characteristics are analyzed. Second, based on the mathematical relationship between condenser parameters and output reactive power, reactive power increment considering saturation parameters is introduced to optimize the reference value of inner ring voltage and outer ring PI control in excitation links in stages. Finally, the reactive power control model of the Ximeng-Taizhou UHVDC transmission system is established, and the optimization effect of the excitation control strategy is verified by simulation. The results provide technical support for the optimal design of the phase modulators, and also play an important role in improving the power grid voltage fault support capacity of the phase modulators and the voltage stability level of China's HVDC power network.