Abstract: The characteristics of ultrasonic plastic soldering were studied.During the soldering the high frequency electric power may be divided into three parts,t₁-vibration causes friction and heating,t₂-components were soldered together,and t₃-the excess power was left over.The soldering strength F increaJses with the power p lost in unit volume.When saturation was reached,the soldering seam will protrude with the electric power was increased again.The study is useful for developing automatic soldering equipment and for improving the ultrasonic plastic soldering.