Aim at cost allocation problem of cogeneration plant products, the paper presents a new heat-electricity product cost allocation method named equivalent allocation method. In the method, the heat-electricity product cost is divided into Fixed Cost and Variable Cost. They are allocated respectively based on the unit type and the equivalent characteristic between heat product and electricity product. Compared with other existent allocation methods, the equivalent allocation method reflects "deciding electricity by heat" principle and market attribute more reasonably. It is observed that the equivalent allocation method can promote encouraging cogeneration's investment, reducing speculation behaviors of cogeneration's corporations and enhancing energy saving in cogeneration's corporations and heat users. It can also provide important reference value to the establishment of two-part heat tariff charged which is vigorously implemented in China.