It has been mainly studied in this paper on brazing of Cu to Al using Al-Si filler metal. The optimized scanning rate of 2.5 mm/s is first obtained through simulating the temperature field of Cu-Al brazing process based on ANSYS software. Then the brazing of Cu-C11000 to Al-3003 using Al-Si-La-Sr filler is carried out by torch brazing technology. It is found that the brazing seam region is mainly consisted of ${alpha}$-Al solid solution and $CuAl_2$ IMC. Further experimental results also show that the rare earth element La in filler metal can not only refine the grain, but also promote the dispersion of intermetallic compounds into the brazing seam, which significantly improves the brazing seam microstructure and mechanical properties of the joints.