The lap joint of commercial purity titanium (TA2) and copper (T2) plates was made via friction stir welding technique. Based on the optimization experiments, the suitable process parameters have been obtained as follows: rotation speed of 800rpm, travel speed of 20 mm/min and rotation speed of 900 r/min, travel speed of 30 mm/min. Under this process conditions, the defect-free lap welds with well formed surface and the interface of joint can be obtained. Using OM and SEM the investigation on the weld characteristics was conducted. Results show that the phenomenon of the flow in the macro scale of Cu and Ti between the joint-interface is exhibited obviously, and the flow amount of Ti to Cu is more than that of Cu to Ti greatly, furthermore, some parts of joint-interface present the typical bounded texture microstructure of Cu and Ti. About 4.8 μm thickness of diffused intermediate layer is formed in the interface of lap joint, the diffusion velocity of Cu is faster than that of Ti, and the lap joint of Cu and Ti has formed the metallurgical bonding