[Objective] To provide important theoretical basis and technical references for the selection of open phase fault diagnosis methods and the formulation of fault-tolerant control strategies for the dual three-phase permanent magnet synchronous motor (DTP-PMSM), this paper investigates the fault characteristics of the DTP-PMSMs with open phase, including the current, voltage, torque, copper loss, and efficiency, as well as the impacts of the faults on the motor. [Methods] Firstly, the vector space completely decoupling control of DTP-PMSM was briefly introduced. Secondly, based on the dual three-phase vector space completely decoupling theory and dual-dq transform theory, the general expression of the current of DTP-PMSM with open phase fault was given by using the symmetric component method according to the asymmetric system characteristics of the motor during the fault. Then, the torque, copper loss, efficiency and voltage in different coordinate systems were systematically analyzed and evaluated and compared with the performance of the motor during normal operation. Finally, experiments were conducted on the DTP-PMSM under both normal and open phase operation, comparing the experimental results with theoretical analysis and simulation results from time-domain and vector diagram perspectives. [Results] The experimental results indicated that when the DTP-PMSM adopted vector space completely decoupling control and experienced an open phase fault, the amplitude of the remaining healthy phase currents increased. The trajectory of iαβ and uαβ in the fundamental subspace became distorted, and the harmonic currents and voltages escalated. At the same time, the DC component of copper loss increased by 38. 09%, the second harmonic torque increased up to 40.76% of its DC component, and the efficiency decreased by 11.85%. [Conclusion] The experimental results validate the correctness of the theoretical analysis and simulation results on the open phase fault characteristics of the DTP-PMSM proposed in this paper, and provide support for subsequent fault-tolerant control and fault detection in DTP-PMSM under open phase fault conditions.