In this article, a fault-tolerant control is proposed for the dual three-phase permanent magnet synchronous machine (PMSM) system in the event of open phase fault. The goal of this control strategy is to minimize the copper loss of the system to the fullest extent while satisfying the load torque demands, thereby boosting system performance. This study utilizes two identical three-phase PMSMs to simulate a dual three-phase PMSM system, adopting a connection manner that isolates neutral points. Initially, the modeling procedure of dual three-phase PMSM and two prevailing control strategies for open phase fault-tolerant control are presented. Subsequently, a control strategy, designated as the transition mode, is introduced. By comparing the three modes, it is manifest that the transition mode can reduce copper loss while meeting the load requirement. Furthermore, in contrast to the minimum copper loss mode, it supplies additional torque while the former mode is unable to operate normally as it fails to furnish sufficient torque. Experimental results substantiate the feasibility of this control strategy.