The apparent resistivity well-observation of Tongzhou station was completed in November 2019,and has been put into practice observation in 2020 after relevant tests have been completed. Before the M_S5.1 earthquake in Tangshan,Hebei Province on July 12,2020 the apparent resistivity showed a certain degree of variations as early as in April,in which the NE and NW observations have been decreasing simultaneously,and the NW observation turned upward since mid-June. The EW observation has a certain rise in the same period,with the variation range is about 1/4 of the NE observation. The focal mechanism solution of this earthquake is strike-slip type. The direction of the maximum principal compressive stress(P axis)is 101°. The angle between the P axis and NE,NW and EW observation is 70°,50° and 10°,respectively. The NE observation dropped the most before the earthquake,followed by the NW observation,whereas the EW observation changed the least,which conforms to the experimental results and the practical observation of that the apparent resistivity anisotropic changes before earthquakes.