The utility model discloses a cutting mechanism for a sugarcane harvester. Including a base, a cutting box is fixedly connected to the left side of the base; a partition plate is arranged in an innercavity of the cutting box. a motor is fixedly connected to the top of an inner cavity of the cutting box through a fixing block; the left side of the top of an inner cavity of the cutting box is movably connected with a rotating rod through a bearing, the bottom of the rotating rod penetrates through the partition plate and extends to the bottom of the partition plate, and the top of the surface of the rotating rod is sleeved with a second bevel gear matched with the first bevel gear. The base, the cutting box, the partition plate, the motor, the first bevel gear, the rotating rod, the secondbevel gear, the rotating shaft, the cutting knife, the cutting hole, the supporting rod, the containing plate, the sleeve plate, the baffle, the groove, the damping spring, the support and the idler wheel are used in cooperation. The problems that the manual cutting speed is low, a large amount of time is wasted, an existing sugarcane cutting mechanism is inconvenient to use, and the production efficiency is reduced are solved.