The invention relates to a method for welding plastic products by utilizing ultrasonic waves, which comprises the following steps: a plurality of ultrasonic rays are arranged on the first bonding surface of a first plastic part, and a wedge-shaped ultrasonic ray melting head is arranged at the lower part of each ultrasonic ray; an ultrasonic groove is arranged on the second bonding surface of a second plastic part, and the bottom surface of the ultrasonic groove is a surface inclined downwards; the first plastic part and the second plastic part are respectively installed in a die, the ultrasonic rays of the first plastic part are inserted into the ultrasonic groove of the second plastic part, and a certain number of gaps for containing rubber are reserved in the ultrasonic groove; an ultrasonic generator is started, the ultrasonic ray melting head of the ultrasonic rays of the first plastic part is melted in the ultrasonic groove of the second plastic part, and the first plastic part and the second plastic part are connected into a whole. The method has the advantages that the ultrasonic rays can be guided to be well melted and connected with the ultrasonic groove, and thus the purpose of firmly welding the two connected plastic parts is achieved; in addition, because of the melting gaps, the problems of rubber leak and distortion are overcome.