in this parer, the author first dealt with the capping bed, the major indices controlling the confining and blocking quality of the caping bed. the grading evaluation of thecapping bed, and the factors affecting the confining capacity of the capping bed. After that,regression analysis was used to find out the correlation between the geophysical characteristics of the capping bed and such factors as breakthrough pressure, permeability, mud contentand porosity under different conditions. Finally, grading evaluation of the capping bed wasperformed on the basis of well logging data.Exemplified by the work in a certain oil field, the present paper points out the feasibilityof applying wall logging data to the study and evaluation of the confining behavior of thecapping bed as well as the fairly good geological effect that can be obtained.