ABSTRACT Presently, many industrial applications of gear sets with skew axes, especially worm gear and hypoid gear, are most widely used. The main content of this thesis is to construct the contact analysis model of the line-contacted type tooth profile of gear sets with skew axes with assembly error. The influence of geometrical parameters of skew-axes gear to the transmission error is analyzed. The complex method for optimization is implemented to select the better skew-axes gear parameters with the best performance in transmission error with assembly error. To prove the presented analysis model, the optimized gear parameters are utilized to construct the solid model for analyzing the contact properties by using computer simulation program.