A synchronous condenser (SC) is used to maintain grid voltage stability owing to its bidirectional fast reactive power regulation ability and good dynamic characteristics. To address the issue of dynamic voltage instability in power system during failures or heavy inductive loads, an SC reactive power regulation optimization method based on single neuron adaptive PID (SNA-PID) combined with whale optimization algorithm (WOA) is proposed. This approach aims to overcome the limitations of normal PID controllers. A simulation model of the SC reactive power regulation system, based on SNA-PID combined with the WOA, is established using Matlab. The parameters of the SNA-PID are optimized by the WOA with the ITAE criterion under two typical operation situations of the power system: one is to set three different degrees of short-circuit ground faults, and the other is to access three different three-phase resistive loads. Compared to conventional PID control, as the degree of short-circuit ground faults increases and the three-phase resistive load resistance decreases, the SC reactive power regulation optimization method based on SNA-PID combined with the WOA can still reduce the voltage recovery time and voltage oscillation, while maintaining voltage stability. Simulation results show that the proposed method exhibits better dynamic adjustment characteristics and adaptive ability.