In order to meet the requirements of high transmission efficiency and low noise in the planetary gear transmission sys? tem， the bending-torsion-shaft coupling power of helical planetary gear transmission system was established by employing the lumped parameter method， with considerations for eccentricity error and installation error. Using the fourth-order Runge-Kutta method to solve the dynamic equation， the dynamic characteristics of the planetary gear， such as the dynamic meshing force， dy? namic transmission error， and dynamic load coefficient， were obtained. Based on this， the planetary gear modification research is carried out， and the tooth profile modification is established. Upon establishing the tooth surface equation and the dynamic equation that takes tooth surface modification into account， an analysis was conducted on the dynamic characteristics corresponding to vary? ing degrees of modification. The research results show that with the increase of the modification amount， the dynamic meshing force， dynamic transmission error and dynamic load coefficient of the planetary gear all decrease to varying degrees， and then in? crease after reaching the lowest value. Performance testing of the entire machine revealed a reduction in vibration and noise of the planetary reducer， as well as an improvement in transmission performance providing theoretical support for the design of vibration reduction， noise reduction and transmission efficiency improvement of the planetary gear transmission system.