In order to solve the problems of large stomata， coarse grain and poor mechanical properties of the aluminum alloy joints， the welding of the 7075 aluminum alloy thin sheet was completed by using the CMT welding method， and the ultrasonic wave was introduced in the welding process.The influence of different ultrasonic power on welded joint stomata， microstructure and mechanical properties were investigated by gold phase，EBSD，and mechanical properties.The results show that ultrasonic vibration can significantly reduce the number of stomata and increase the melting width， and the width of HAZ decreases with the microhardness of welding joints at 1200W by about 8.93HV， tensile strength 5by about 85MPa and fracture elongation by 1.4%.According to EBSD results， the average grain size of the weld was 36.89 μm when the ultrasonic power is 1200W，9.99 μm and the large angle boundary ratio of the welding joint to some extent.