Pitch deviation, a type of longwave deviation, has been demonstrated to be a significant contributor to noise generation in the drive trains of motor vehicles operating at relatively high speeds. To date, numerous studies have investigated the effects of pitch deviation on the dynamic characteristics of gear systems. However, these models often exhibit inconsistencies with real-world observations due to the simplification of the contact between teeth pairs. This simplification ignores clearance compensation and damping of the oil film. To fill this gap, a new numerical model of spur gear systems with pitch deviation considering lubrication is proposed. An analytical model of the time-varying mesh stiffness (TVMS) and meshing impact force for spur gear pairs is proposed, in which the geometric relationship and iterative solution process are investigated. An improved tribodynamic model is established to investigate the excitation behavior of gear pairs with pitch deviation under lubrication. The accuracy of the proposed model is verified through comparisons with references and experimental results. The results show that the random impact phenomenon of the TVMS is significantly suppressed by the oil film, and the meshing impact force is also reduced. The transmission stability of spur gear pairs with tooth pitch deviation is improved under lubrication. The research results provide theoretical support for accurately predicting the dynamic responses of spur gear pairs with different precision levels while considering lubrication.