Lip seals are crucial for preventing lubricating media leakage and intrusion of abrasive particles into rotating shaft oil tanks. While numerical simulations have advanced understanding in oil-lubricated conditions for lip seals, grease's rheological complexities hinder accurate modeling. To address this limitation, this study proposes a novel fluid-solid coupling model tailored specifically for lip seals operating under grease lubrication conditions. By integrating deterministic surface topography, thermal characteristics of seal working area and flow separation method, the model achieves precise solutions for seal performance parameters. Experiments validate this model, elucidating the effect of grease and operating parameters on characteristics such as friction torque and leakage rate. This research advances lip seal analysis, offering insights for optimizing grease lubricated lip seal systems.