In order to solve the problems of low production efficiency and hidden safety in manual assembly, an automatic assembly system for adjustmentjoint assembly was developed based on programmable logical controller(PLC).The composition and assembly method for the adjustmentjoint assembly were introduced, and the overall structure, function and the automatic assembly process of the system were described. With SIMENS S7-200 SMART PLC as the control core, HMI as the interaction bridge between human and systems, and the electrical and pneumatic transmission as the driving force,the hardware selection and software programming design of the electrical control system were completed.By using the system, automatic assembly of adjusting joint components is realized with high efficiency, high quality and safety