For improving assembly quality and automation of electric connectors, a solution of automatic assembly is discussed in this paper. With the machinery vision system, defects of the parts to be assembled can be real-time surveyed. By using the complex image recognition technology, the recognizing accuracy and reliability can be achieved. The designs of NC dividing head and smart positioning unit can make the process of transmission and assembly more perfect and effective. The optimal design of the mechanical structure has been made by virtual prototype technology. The designs of PLC control system and pneumatic system which are used in the automatic assembly machine have also been discussed. The control strategies of assembling process are quite challenges. The control profile of three stages has been used in the pressing assembly process, which can punch the parts assembled properly and smoothly without any surface damage. Also the application shows that the design is effective.