Abstract: In view of the unloading height requirements of the coal mine underground roadway repairing machine under the limited roadway height, the structure of backhoe working device was determined. The kinematic model of the working device was established based on the Denavit-Hatenberg homogeneous transformation matrix. The position expression of the bucket tooth tip in the coordinate system is derived, and the spatial constraints of backhoe working devicewere determined. Aiming at improving the digging force of the whole machine, and using the working space limitation of the roadway repairing machine as a constraint condition, the genetic algorithm was used to optimize the working device. The optimization results show that the excavation force of the backhoe working device increases by 9.4%; the length of boom is shortened by 8.9%, the length of intermediate arm increases by 47.9%,the length of arm is shortened by 18.7% and the total length of the working device is shortened by 3.6% to cost savings. It is clear that space constraints have significant effects on design variables and digging forces.