Abstract: We have discovered many oil and gas fields with carbonate reservoirs. Owing to the uneven distribution of pores in the carbonate rocks and the special character of mud invasion, we have encountered many difficulties in the application of the conventional theories and methods for the evaluation of the oil and gas formations. In recent years, we have studied the structures of pores in the carbonate rocks, the character of mud invasion and the method of well log interpretation. By the application of the variable exponent of pore structures and the concept of "partition type" of mud invasion, integrated with the well log interpretation methods to determine the porosity and water saturation of the carbonate reservoirs, the accuracy of interpretation has been improved. The presence of oil and gas within the detection range of the well logging instrument is the basis of well log interpretation. With this idea in view, this article mainly discusses the well log interpretation method for three types of carbonate rock porosity: interstitial porosity, mixed porosity and porosity in fractures. Examples are given for illustration.