The invention discloses a spiral bevel gear cutting machine tool and a gear cutting method. The gear cutting machine tool comprises a cutting tool system, a workpiece system, a machine tool body and a numerical control system, wherein the cutting tool system comprises an XZ working table, an X-axis lead screw, a Z-axis lead screw, a short shaft, a tool base revolving drum, a tool base, No.1 milling cutters, a milling cutter shaft, No.2 milling cutters, a gear shaft and a correcting wedge. The rotating centre line of the tool base revolving drum and the rotating centre line of the short shaft are collinear; the right end surface of the tool base revolving drum is fixedly connected with an annular flange plate at the left end of the tool base by the correcting wedge; the right end of the tool base is provided with the milling cutter shaft; the rotating centre line of the milling cutter shaft and the rotating centre line of the short shaft are intersectant; and both ends of the milling cutter shaft are provided with the No.1 milling cutters, the No.2 milling cutters or grinding wheels. The left end surface of the tool base is provided with a drive motor; the drive motor is meshed with a bevel gear on the milling cutter shaft by the gear shaft; and the rotating centre line of the output shaft of the drive motor and the rotating centre line of the milling cutter shaft are vertically intersectant. The invention also provides a method for processing helical bevel gears by utilizing the machine tool.