Abstract: A new way of ultrasonic-assisted soldering with ultrasonic precoating process based on the microstructure of the intermetallic compounds was proposed, in order to study effect of the microstructure of interface intermetallic compound layer of copper/aluminum dissimilar metal soldering joint used Sn-9Zn system eutectic filler metal on the mechanical properties of the joint. Intermetallic compound layers formed between copper and solders were crushed into fine particles and scattered in solder with this new way. Tensile strength of the joints was improved extraordinarily, and even more than the tensile strength by traditional process when the intermetallic compound layer thinned to minimum thickness (1-2μm). A new method of the microstructure of the intermetallic compounds control based on ultrasonic-assisted soldering with ultrasonic precoating process was proposed. The evolution rule of compounds in the soldering process was studied, and the influence of the structure and distribution of the intermetallic compound layer on the mechanical properties of the joints were discussed.