The invention relates to a clamp for processing a gearbox body of a forklift. The specific structure of the clamp is that a left pressing plate mechanism, an intermediate mechanism and a right pressing plate mechanism are correspondingly arranged on a bottom plate, wherein a first locating pin and a second locating pin are correspondingly arranged on the bottom plate parts at two sides of the intermediate mechanism; the left pressing plate mechanism comprises an arc-shaped pressing plate and a left pressing plate; the right pressing plate mechanism comprises a locating pressing plate and a right pressing plate; one side of the gearbox body to be processed, of the forklift, is a differential housing and the other side of the gearbox body to be processed, of the forklift, is a motor mounting housing; when the clamp is put into use, the gearbox body to be processed, of the forklift, is positioned on the first locating pin and the second locating pin, the arc-shaped pressing plate and the left pressing plate are pressed to the top part of the differential housing, the right pressing plate is pressed to the top part of the motor mounting housing, and the locating pressing plate is pressed onto a lug on the motor mounting housing, so that the gearbox body to be processed, of the forklift, can be positioned and clamped. The clamp is reliable to locate and compress; the problem of vibrating in processing can be solved; the one-point compressing in the prior art is adjusted to be multi-point compressing, thereby removing the influence of human factors on the workpiece clamping effect.