The utility model belongs to the ultrasonic detection technology, and relates to a small-diameter bar ultrasonic detection tool, which is characterized by comprising a bar guide sleeve, a probe positioning sleeve, a gasket and an elastic pressing sheet, wherein a mounting through hole is formed in the side wall of the guide sleeve, the mounting through hole is a stepped hole, the gasket is arranged on the stepped surface of the stepped hole, the probe positioning sleeve is fixed in the mounting through hole, the aperture of a central hole of the probe positioning sleeve is smaller than or equal to that of the central hole of the stepped hole, and the probe positioning sleeve is used for sleeving an ultrasonic probe; an elastic pressing piece is fixed to the outer wall face of the bar guidesleeve and used for pressing the ultrasonic probe into the probe positioning sleeve. The guide sleeve tool component can be replaced according to the diameter of a small bar, the tool is simple in structure and convenient to operate, time can be effectively saved, productivity is improved, and the guide sleeve tool component has high practical application value.