Quantitative estimation of undiscovered mineral resource has been an important step in resource assessment. The resource estimation method by metallogenic geological bodies is the improvement of the traditional volumetric estimation. The authors infer that the mineralized geological bodies of the same size have the same quantity of resources. Ore-bearing coefficient of the control area (the model area) can be calculated by two parameters, i.e., the volumes of the metallogenic geological bodies and the total resource. Through extrapolation by similar analogy, we can estimate the resource of the prognostic area using the volumes of metallogenic geological bodies and ore-bearing coefficients. The delineation of the mineralized geological body plays a decisive role in the method. For potash bearing geological bodies, it needs the guidance of the theory for potash formation in the basin. Such factors as the lithofacies paleogeography, the structure of the sedimentary formation, the stratigraphic isopach and the seam distribution are also well considered, The method was applied to estimating potash resource in the Lanping-Simao basin.