The invention discloses a boring machine boring bar support boring bar centering device comprising a cone bearing, a cone bearing left end cover, a cone bearing inner fixed sleeve, a left back nut, a left adjusting thread bushing, a nylon tapper sleeve, a boring bar support upper half pressure cover, a cone bearing right end cover, a positioning square key, a right back nut, a right adjusting thread bushing, a keyway nut, a fastening screw, a cone bearing outer fixed sleeve and a boring bar support fixed pedestal; in working, the left and right adjusting thread bushings cannot change position, and thus avoiding affecting the gap between the nylon taper sleeve and the boring bar; the outer taper degree of the nylon tapper sleeve is reduced from 8 to 2 degrees, thus reducing nylon taper sleeve radial pressure on the boring bar, and the boring bar cannot be tightly extruded.