The present invention aims at providing a small-diameter wire/rod/tube ultrasonic detector with an end blind area and an automatic ultrasonic nondestructive detecting system, wherein a sealing cover of the ultrasonic detector is located on a water storage device; an annular array unit mounting rack and a water pump are fixed in the water storage device, and an annular array detecting unit is connected to the annular array unit mounting rack; the water pump is connected to an input end of water circulation input and output; a sensor is mounted in one side of the sealing cover in which a detected material is allowed to enter; the annular array detecting unit comprises an outer ring part and an inner ring part, and the outer ring part and the inner ring part are connected into a whole by means of a wire inlet side end cover and a wire outlet side end cover; the outer ring part consists of an outer ring substrate and an outer ring arraying probe, and the inner ring part consists of an inner ring inner core and an inner ring inner core locking ring. The ultrasonic detector in the present invention has unique “acoustic eye” structure characteristics, changes the mode of ultrasonic waves entering the detected material, and can effectively eliminate the end detection blind area of the wire/rod/tube.