Abstract: The main problem of friction stir welding(FSW) applying in industry is the lower joint strength coefficient as welding work hardened materials.The influence of welding heat on the joint strength was analyzed.The friction stir welding process with forced cooling was researched.The influence of forced cooling on the surface modality,hardness distribution and joint strength of FSW joint of copper plate were compared.The approximate mathematic expression of the temperature during the forced cooling friction stir welding process was built up.The research results show that:the forced cooling during FSW of copper can decrease the temperature of weld zone and heat-mechanical affected zone during welding,minimize the soft zone width and weak degree,and increase the properties of FSW joint.With the optimized rotary speed 1 500r/min,moving speed 0.3 mm/s,and forced cooling,the tension strength of copper welded joint is 269 MPa.