Statistics methods are often used in the oil-gas resource evaluation，mainly include scale sequence method，discovery process model method and generalized Pareto method. But reservoir number is hard to be determined during the process of oil-gas resource evaluation. In order to calculate the oil-gas resources more accurately and reasonably，the undiscovered large and medium-sized reservoirs were predicted by the trap additivity first. Then the overall number of pools was calculated by using the reserve scale sequence of large-medium-sized reservoirs both including discovered and undiscovered. At last，according to the number of pools，the oil-gas resources were calculated in this area by the multi-statistics method. This method can solve the problem that the number of pools is difficult to confirm，and it can enhance the accuracy of the results of oil-gas resource calculation.