Abstract: An automatic control device of contact force for electro-spark deposition was designed to study the influence of contact force on electro-spark deposition. Automatic deposition with different contact forces was tested. The deposition efficiency, mass transfer efficiency, surface morphology of deposited layer and the number of various discharge waveforms under different test conditions were analyzed. The results show that when the contact force is 1.0 N, the maximum deposition efficiency and mass transfer efficiency are achieved, and the surface quality of the deposited layer is also good. The automatic control device for the contact force of electro-spark deposition can maintain the contact force between the electrode and the workpiece, so as to keep automatic electrode feeding. The change of contact force will change the contact status between the electrode and workpiece. With the increase of the contact force, sparks and splashes produced in automatic deposition decrease, and the short-circuit discharges increase while the contact discharges decrease, thus affecting the automatic deposition efficiency and the quality of deposited layer. Under certain test conditions, selecting the appropriate contact force can improve the deposition efficiency and mass transfer efficiency, and obtain a better quality of the deposited layer.