The peak short-circuit current of a megawatt-class generator unit can reach hundreds of kiloamperes. The generator outlet circuit breaker (GCB) is installed between the generator and the main transformer. It needs to maintain its structural stability under extreme short-circuit electrodynamic loads. The strut insulator, as the support structure of the circuit breaker, has a direct impact on the dynamic stability of the whole machine. Based on COMSOL, this paper constructs a six-channel parallel type vacuum generator outlet circuit breaker model, reveals the stress distribution characteristics of the pillar insulator ceramic column. It proposes the stress optimisation method from the aspects of insulator size, quantity, spacing, support angle and upper support structure. Simulation results show that: the column stress is nonlinear decay with increasing radius, and the decreasing trend tends to be stable; insulator quantity increase, spacing reduction, support angle increase and the upper support structure can reduce the column stress, but the effect of these factors is weaking as the radius increases. The study provides a theoretical reference for the dynamic stability optimal design of GCB column insulators.