This paper aims to study the factors affecting transmission efficiency of ball-type constant velocity joint (CVJ) from a mechanistic perspective. Based on various efficiency loss mechanisms and proportions, optimization design methods for improving transmission efficiency of ball-type CVJ are proposed. (1) To design a ball-type CVJ with cross track shape so that the combination of each ball pop-up force is approximately 0 under normal working angles. (2) To adopt 8-ball ball-type CVJ instead of 6-ball in order to reduce vertical load between balls and tracks, thereby lessen friction. (3) To optimize the clearance tolerance range between ball and cage window to increase ball-type CVJ rotational backlash in condition of meeting NVH requirement. (4) To use low friction grease. Finally equipment and method for transmission efficiency testing of ball-type CVJ is presented. Various ball-type CVJs are made for transmission efficiency measurement, to verify the effectiveness of transmission efficiency improvement methods proposed in this paper.