A tool bit replaceable rotary cutting tool, comprising a tool bit and a tool bar, the tool bit being detachably connected with the tool bar, the tool bit and the tool bar having the same axis, the tool bar being provided with a blade portion and a shank portion along the axis and the blade portion being connected with the tool bit, wherein the tool bit comprises a cutting edge, a chisel edge chip removal surface, a contact surface, a tool bit screw hole, a circumferential cutting margin, and a central positioning cylinder, wherein the cutting edge and the chisel edge chip removal surface are arranged at the top of the tool bit, the contact surface and the circumferential cutting margin are arranged on the lateral surface of the tool bit along the axis, wherein the central positioning cylinder is arranged at the bottom of the tool bit; the tool bar comprises a chisel edge avoiding surface, a torque support surface, a screw hole, a central positioning hole, a cooling passage, a cooling hole, two cooling guide grooves, a main chip groove and an auxiliary chip groove, the chisel edge avoiding surface is connected with the chisel edge chip removal surface, the chisel edge avoiding surface and the chisel edge chip removal surface are converged with the main chip groove and/or the auxiliary chip groove, the torque support surface contacts with the contact surface, the screw hole is formed in an end portion of the tool bar in the penetration manner, a screw penetrates through the screw hole and the tool bit screw hole to fix the tool bit to the tool bar, the central positioning hole forms positional correspondence with the central positioning cylinder, the central positioning cylinder is positioned in the central positioning hole, and a depth of the central positioning hole is larger than an axial length of the central positioning cylinder; the tool bar is provided with the at least one main chip groove and one auxiliary chip groove along the axis, an internal helical angle of the main chip groove comprises a first helical angle and a second helical angle, and the main chip groove extends to the cutting edge of the tool bit; and the cooling passage for delivering a coolant during drilling is formed in the tool bar, and the cooling hole is formed in one inner end of each cooling guide groove; the rotary cutting tool being characterized in that the tool bit further comprises a convex V-shaped positioning surface, wherein the tool bit screw hole is formed in the tool bit in a penetration manner and penetrates through the contact surface and the convex V-shaped positioning surface is arranged at the bottom of the tool bit; the tool bar further comprises a concave V-shaped positioning surface, wherein the screw hole penetrates through the torque support surface, the concave V-shaped positioning surface forms positional correspondence with the convex V-shaped positioning surface, a protruding portion of the convex V-shaped positioning surface is positioned in a recess portion of the concave V-shaped positioning surface, the convex V-shaped positioning surface contacts with the concave V-shaped positioning surface, an angle of the first helical angle is different from an angle of the second helical angle, and the two cooling guide grooves distributed along a direction of the axis are formed in an outer wall surface of the end portion of the tool bar.