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 . <EOS>