The invention relates to a determining method of the mixed ratio of high-heat evolution basin mixed source natural gas, and belongs to the technical field of oil gas exploration and development. According to the distinguishing characteristics showing different kinds of gas reservoirs in a targeted region, the hydrocarbon source rock pyrolysis simulation experiment results are combined for determining the type of the gas reservoirs in the targeted region; on the basis, master standards of two kinds of gas reservoirs of the coal gas Y and the oil type gas Q of the targeted region gas reservoirs and methane carbon isotopic of the master standards can be determined; the linear relationship between the mixed ratio of the mixed gas and methane carbon isotopic delta 13C 0.1 percent of the mixed gas obtained after mixing the coal gas Y master standards and the oil type gas Q master standards is built; according to the linear relationship, the methane carbon isotopic value of mixed source gas H is compared for determining the mixed ratio of each single-well mixed source gas. The method provided by the invention has the advantages that the precise proportioning of different sources of the mixed source gas reservoirs can be divided; the precision is high; the problem that the mixed source gas cannot be quantified in the prior art is solved; the exploration direction of the deep layer natural gas is greatly improved; great technical support is provided for the deep layer natural gas exploration and development strategy region selection.