The invention relates to a gas box assembly fixture. The gas box assembly fixture comprises a device frame; a clamping arm installation base of which the rotary axis extends in the horizontal direction is rotationally assembled on the device frame; two gas box clamping arms are movably assembled on the clamping arm installation base; each gas box clamping arm is provided with at least two fixed connecting structures used for being detachably fixed to gas box studs or threaded holes in a gas box in a spaced mode in the horizontal extending direction of the gas box clamping arm; and the two gas box clamping arms have clamping positions close to each other and further have releasing position away from each other. Each box clamping arm is provided with at least two fixed connecting structures used for being detachably fixed to the gas box studs or the threaded holes in the gas box in the spaced mode, and thus the gas box can be stably supported; the left side surface, the right side surface or the top surface of the gas box can be conveniently and reliably turned to the downward position by being matched with rotating of the clamping arm installation base around the horizontal axis; and operation is convenient, and the assembly efficiency of the gas box can be effectively improved.