Abstract: The article mainly discussed the microstructure's state of weld and HAZ by mechanical vibration(frequency of vibration is among 33166Hz)welding process.The 16MnR steel commonly used in vessel was used in the experiment.It was welded by SAW while it was being vibrated mechanically in low frequency.Three samples weres separately welded in various frequency and amplitude of vibration.The results show that the mechanical vibration welding can largely improve the microstructure of weld and HAZ,the size of grain of weld was obviously refined,the weld line and over heated zone were narrowed,and the dimension of widmanstatten structure in HAZ was greatly decreased.Meanwhile,the forming process of weld and HAZ in the current situation was discussed in detail from the point of view of weld pool solidifying process and temperature field.It was also included that the frequency of vibration had not effective effect on the microstructure of weld and HAZ in narrow scope.The mechanical vibration welding had larger effect on the microstructure of weld and HAZ.