Abstract: Resistivity is one of the important physical parameter of rocks. It plays an important role in analyzing the intrinsic properties and occurrence conditions of rocks. The paper chooses sandstone, limestone, mudstone and granite as representing rocks to analyze the resistivity curve during loading progress. Through the analysis, the critical point of resistivity was found. And the stress ratio of the critical point is 70%~85%, corresponding to the yield point in rocky strain. And the directivity of critical point was found at the same time. The critical point found from the study can be used to judge yield point and the strain state.