The invention relates to the technical field of machining, and discloses an inclined hole machining method. The inclined hole machining method comprises the specific steps that S1, the offset distanced0, relative to a to-be-drilled inclined hole, of a centering hole, and the penetration depth h0 of the centering hole are calculated; S2, a workpiece is clamped, and the centering hole is machined according to the offset distance d0 and the penetration depth h0; S3, an abutting surface is machined, a channel defined by the abutting surface and the surface of the workpiece is made to communicatewith the centering hole and extend towards the intersection point between the to-be-drilled inclined hole and the surface of the workpiece, the abutting surface is parallel to the axis of the to-be-drilled inclined hole, and the distance between the abutting surface and the axis of the to-be-drilled inclined hole is equal to the radius r2 of the to-be-drilled inclined hole; and S4, the to-be-drilled inclined hole is machined according to the preset radius r2 of the to-be-drilled inclined hole and the preset drilling depth h1. Due to the fact that the abutting surface is machined, the peripheral surface of a drill bit can abut against the abutting surface, drilling offset or tool bending is not prone to occurring in the inclined hole drilling process, and accordingly, the precision of the inclined drilled hole formed in the outside of an air cylinder cover combustion chamber is high.