Abstract: With the development requirements of product lightweight,laser transmission welding of plastics is becoming a research focus,since it has good welding quality,controllability and is able to weld tiny parts.This paper discussed the effects of welding process factors,such as laser power,welding speed, clamping force and absorbent,on laser transmission welding of PP,using an 808 nm semiconductor laser.The shear strength of the joint was tested and the microstructure was examined after welding.The experimental results show that there was a proper range for welding heat input to obtain good weld formation and joint strength while keeping the clamping force and laser spot size constant.