Diamond/AlSi composite coatings were prepared on Ti-6Al-4V alloy matrix by ultrasound-assisted brazing coating technology. The effects of ultrasonic brazing process parameters on the microstructure of diamond/AlSi brazing coating were investigated. The interfacial reaction mechanism between AlSi filler metals and diamond on the matrix under ultrasonic action was discussed. The results show that TiAl₃ compounds and a large number of Ti(Al_1-xSi_x)₃ compounds are mainly formed in the contact interface between titanium alloy matrix and AlSi filler metals. The growth of Ti(Al_1-xSi_x)₃ is mainly affected by the interfacial reaction and the diffusion rate of atoms to the reaction site. Ultrasonic treatment can improve the wetting and spreading effect of AlSi filler metal on the matrix by cavitation effect to achieve the wetting of diamond particles by inactive AlSi brazing filler metal. The mechanism is that the intermetallic compound Ti(Al_1-xSi_x)₃ is formed at the interface between AlSi filler metals and the substrate. Ti(Al_1-xSi_x)₃ is broken and dispersed throughout the brazing coating by ultrasonic cavitation and acoustic streaming effect, ultimately leading to the reaction of Ti, an element in the titanium alloy matrix, with diamond to form TiC.