The work aims to apply finite element simulation to surface cracks of Q235 steel based on principle of potentiometric detection. Firstly, several schemes consisting of different width, different depth and different angle between crack and excitation were designed firstly for simulation calculation. Secondly, analytical solution based on the principle of DC-bit method and finite element simulation were compared and validated to verify accuracy of the finite element simulation. For surface cracks of different width, potential values on both sides were different, there was obvious extremum inflection point, and voltage drop on both sides became gentle as the crack width increased. Potential amplitude on both sides increased with the increase of crack depth, and minimum detectable crack depth was 0.02 mm. Density and trend of electric field lines were different around the cracks in different directions. When 30o≤α≤90o, the surface crack could be detected in the DC potential method smoothly. The finite element simulation results were verified based upon analytical solution, trend of potential signal at the cracks was consistent, the amplitude was slightly different, hence the results were reliable. The DC potential method has higher resolution in detecting different width, different depth and different angle of the surface cracks of Q235 steel, which provides a certain feasibility basis for detecting surface cracks of Q235 steel in potential method, and is of significant engineering practical value.