Harmonic drive is an indispensable device for robotic joint, and transmission accuracy of harmonic drive is one of its most important performance indexes. Due to the unsystematic research on the accuracy of harmonic drive, the accuracy consistency of harmonic drive is poor, and the prediction accuracy is seriously insufficient. This study focuses on modeling of transmission error system and prediction of transmission accuracy. Through tracing analysis of transmission error of harmonic drive, a transmission error model including manufacturing, assembly and tooth profile error is established. Based on Rayleigh distribution of error sources and considering multi-tooth meshing effect of harmonic drive, the transmission accuracy prediction model is built. Tooth profile error is measured by gear measuring center, dimension error and geometric tolerance are gauged by coordinate measuring machine. The transmission accuracy of three types harmonic drive (SHG14, SHG20 and SHG25) is measured by harmonic transmission error test bench under rated conditions. The comparison results show that the difference between the predicted and experimental values is less than 15%, which proves the validity of the accuracy prediction model. Prediction method play a crucial role for accuracy control of harmonic drive system.