The invention provides a machining process for machining a bolt carrier by means of a three-axis machining center. After performing rough machining on the bolt carrier, performing fine machining on the outer circle, an end surface A and an end surface B of a rod part and drilling a bolt hole and a spring hole, the bolt carrier is clamped for being machined in a manner that the bolt hole, the spring hole and the end surface A of the bolt carrier are used for positioning, the end surface B is used as a clamping position and the outer circle of the rod part is used for performing auxiliary positioning, and nine processes are performed on the bolt carrier. According to the machining process, a rotating shaft which is composed of a 135 tail support and a 135 dividing head is added for realizing rotation of the machining clamp. Furthermore a cylinder is used for settling a workpiece clamping problem. A positioning base and a base are arranged for supporting the weight of a workiece. One surface and two pins are used for positioning; one pin is a push rod head which is machined to a rhombic member for eliminating over-positioning; one surface is the end surface of the push rod; and the other pin is a reference pin. All machining surfaces are exposed in the machining area of the machining center, so that multiple machining processes are finished in one clamping, thereby reducing clamping time, reducing an accumulated error caused by reference change, improving surface quality, and effectively improving machining efficiency and production efficiency.