Abstract: Motor current monitoring systems have garnered significant attention due to their non-invasive and cost-effective advantages. However, conventional current spectrum analysis is susceptible to inherent harmonic and installation errors, and the high amplitude of the fundamental frequency can obscure fault characteristics. To reveal the frequency modulation patterns in motor current caused by reduced meshing stiffness due to gear faults, a motor current model incorporating faulty gear meshing stiffness is established, and its instantaneous frequency expression is derived. Addressing the limitation of traditional time-frequency analysis methods, which often suffer from low instantaneous frequency estimation accuracy, this paper proposes an instantaneous frequency polar view method based on high-order synchrosqueezing transform (HSST) for extracting gear fault features. This method intuitively demonstrates gearbox faults by detecting frequency modulation characteristics that are synchronized with the meshing period of faulty teeth. The instantaneous frequency polar view effectively avoids interference from inherent harmonics and fundamental frequency, offering a unique representation of gear fault characteristics. Analysis of motor current signals from an RV gearbox test rig validates the accuracy of the proposed motor current model and the distribution patterns of fault characteristics. It also confirms the effectiveness of the instantaneous frequency polar view method based on HSST for gearbox faults diagnosis.