The surface resistivity measured at the Tongzhou station changes before and after the Tangshan M7.8 earthquake in 1976,and the similar resistivity changes from small well were also detected before the Tangshan Guye M5.1 in 2022 and the Tangshan Luanzhou M4.3 in 2021. In this paper we study the change mechanism of resistivity based on the tectonic surrounding the Tongzhou station,measuring ability of resistivity and the characteristics of medium-strong earthquake. The results show that the resistivity changes of Tongzhou is sensitive to the moderate and strong earthquake in Tangshan region,the small well resistivity is more significant changes before and after the earthquake than surface resistivity.