Abstract: Predictive control based on boundary limitation is an effective low switching frequency method for motor control. This paper studies the phenomenon that the PMSM cannot start normally when it adopts the bounded-form method, and puts forward an improved method. First, the causes of the phenomenon are studied, and the conjecture that the starting torque current limit exists in the conventional method is proposed. That is, when the starting torque current is too large, all voltage vectors cannot make the current trajectory enter the boundary, so the motor cannot start normally. Then, the starting current trajectories under all effective voltage vectors are analyzed, and the conjecture of the starting torque limit is verified. Then the general form of the starting torque limit is worked out, and the correctness of the limit value is verified by simulation. To solve the problem of limited starting torque, an improved voltage vector optimization strategy is proposed. When all voltage vectors do not meet the requirements, it is switched to the voltage vector that can reduce the current error maximumly, so as to ensure the normal start of closed-loop speed regulation. Simulation and experimental results show the effectiveness of the improved method, and comparative experiments demonstrate the superiority of the proposed method at low switching frequencies.