Isothermal adsorption tests on shale always yield abnormal maps. On the basis of summary of the abnormal types, the study to probe the abnormal reasons is carried out and corresponding strategies are proposed. When the pressure is high, the methane in reservoir conditions is in supercritical state,the Langmuir model which is based on the condensation mechanism is no longer suitable to describe the adsorption features. This problem can be solved by amending the model or revising test data. When the pressure is low, the disorder on the measurement is caused by the adsorbed gas content in shale that is far lower than coal-bed gas,while the clay mineral content is much higher than that in coal-bed. In order to eliminate the disorder, the sample weight should be more and the sample preprocessing procedures should be amended.