This paper develops an improved hybrid field model (IHFM) to predict the on-load performance of interior permanent-magnet (IPM) motors considering both iron saturation and slotting effect. It combines the air-gap analytical model based on modified conformal mapping with the reluctance mesh method for stator and rotor. The reluctance mesh method can accurately predict the rotor saturation and tooth-tip saturation even their field distribution is complicated due to armature reaction. Besides, IHFM will significantly accelerate computation speed using analytical model for air-gap region while keeping high accuracy. The finite-element analysis and experimental results of flat-type and V-type IPM motors are demonstrated to verify the effectiveness of the proposed model.