The paper studies on the allocation of compensation for ecological benefit of water source protection forest of Beijing Tianjin and Hebei cooperation, introduces the background and problems of compensation for ecological benefit of water source protection forest of Beijing Tianjin and Hebei cooperation, analyses the necessity of ecological benefit compensation allocation, sets up an accounting index system of ecological benefit compensation allocation in Beijing Tianjin Hebei cooperation of water source protection forest, and makes an empirical research which takes Chao Bai river water system as an example. The conclusion is that the ecological benefit of water source protection forest of Beijing and Hebei cooperation?exists the spillover effect evidently which means that compensation for ecological benefit should be allocated by both Water-Receiving?Area and Water?Source?Area, because the ecological benefit of water source protection forest exists the?positive?externality. The paper calculates the maximum of compensation for ecological benefit which the Water-Receiving?Area should undertakes, and also concludes that the allocation coefficient should changes dynamically in the compensation for ecological benefit of water source protection forest.