This paper investigates the issues of current surge and torque ripple during the switching of different modulation modes in segmented synchronous modulation, and proposes an optimal switching point selection strategy based on the stator flux trajectory. The method performs offline reconstruction of the stator flux trajectories during modulation transitions, utilizes the three-phase voltage sequence at the transition instant to calculate three-phase stator flux deviations, and determines the optimal switching point by integrating segmented synchronous modulation principles. This switching strategy eliminates the need for extensive theoretical analysis of harmonic currents in different modulation modes, and can calculate the three-phase stator flux vector deviations solely by utilizing the modulation ratio at the switching instant, which simplifies the switching algorithm. The experimental based on RT-BOX results demonstrate that the strategy ensures negligible inrush currents and torque ripples during modulation mode transitions, confirming the validity and effectiveness of the proposed switching strategy.