The typical sample investigation on the project areas and continuous observations of evaluation indexes in ecosystem service function frame on the Grain for Green Project in Beijing were conducted by Beijing Academy of Forestry and Pomology Sciences. The material quantities and the values of the ecological benefits of the Project were quantitatively assessed and analyzed by six functional evaluation indexes of water storage, carbon fixation and oxygen release, soil conservation, nutrients accumulation, atmospheric purification and biodiversity protection, according to the National Standard of the People's Republic of China "Specifications for Assessment of Forest Ecosystem Services"(GB/T 38582-2020) and the Forestry Industry Standard of the People's Republic of China "Specification of Monitoring and Evaluation of Ecological Benefits of Grain for Green Project"(LY/T 2573-2016), respectively. The results showed that the total value of ecosystem service function for Grain for Green Project by 2018 was 1.892 billion yuan per year in Beijing. The water storage (41.15%), carbon fixation and oxygen release (26.73%) and atmospheric purification (17.27%) those were embodied in the evaluation index frame for the Project contributed larger proportions to the total value of ecosystem service function for the Project. The covered areas and the functional orientations of administrative districts from Beijing City Master Plan are proven to be the main influential factors to evaluate the values of ecological benefits in the districts involved in the Project. Miyun District had the largest value of 448 million yuan per year, accounting for 25.56% of the total value of the ecosystem service function for the Project. The values of ecosystem service function contributed by Castanea spp. (29.51%), Armeniaca spp. (13.54%) and Juglans spp. (12.57%) were on the value list of the first three. The values per unit area of different forest types were as follows: ecological forest > eco-economic forest > fresh fruit forest. Therefore, it is suggested to formulate the protection policies for the achievements of Grain for Green Project following the principles of ecological priority, matching trees with the sites, and classified implementation. The amounts and durations of ecological compensation can be determined according to the evaluations on the values of ecosystem service functions for each district. It will lay the foundations on the theories and practices for the establishment of classification compensation policies, the improvement of low quality and low efficiency forests and the construction of ecosystem monitoring network systems for Grain for Green Project in Beijing.