The invention relates to an adapter for connection of a power transformer bushing tap. The adapter comprises an adaptive binding post and a tap protective shell. The adaptive binding post is provided with a cable connection end and an inner thread connection end adapting to the power transformer bushing tap. The tap protective shell is provided with a barrel-shaped protective shell body and a rotary knob type cable connector. The rotary knob type cable connector penetrates through the bottom of the barrel-shaped protective shell body to be fixed. A connection turnup is formed at the edge of the open end of the barrel-shaped protective shell body. An annular groove is formed in the connection face of the connection turnup. A sealing ring is embedded in the annular groove. The connection turnup is provided with a connection bolt. The adapter is used for connecting the existing power transformer bushing tap with a bushing tap state monitor sensor uniformly, conveniently, rapidly and reliably, and the problems that connection modes of existing connecting pieces for connecting the existing power transformer bushing tap with the bushing tap state monitor sensor are different, the connecting pieces are not convenient to replace or maintain, and the tap connection end protection performance of the connecting pieces is poor can be solved effectively.