The Grain for Green program is the largest ecological construction project in the world thus far and has played an important role in ecological restoration in China. Taking the middle reaches of Heihe River as the study area, we evaluated ecosystem services, such as water conservation, soil conservation, and gas regulation, and calculated their increment after returning farmland to forest. After combining opportunity cost and service increment, the minimum data approach was used to deduce the compensation curve for returning farmland to forest. According to the three scenarios of policy objectives, we compared the compensation standard, proportion and scope of returning farmland, and the increment in ecosystem services in different situations. The results are as follows: ① Conversion of farmland to forest contributes to improving the capacity for ecosystem services. The ecosystem increment of water conservation, soil conservation, and carbon sequestration per unit area was 8.87 mm/m², 105.67 kg/m², and 43.16 g/m², respectively. ② If ecological compensation is not carried out, only 1.42% of farmland would be returned to forest. When the compensation standard reaches 4381.35 yuan/hm², 5.17% of farmland plots could be returned to forest, all of which are suitable for forest growth. When the compensation amount is 7500 yuan/hm², 13.98% of farmland can be returned, and most of the plots are suitable for forest growth. If the compensation standard is 2803.06 yuan/hm², the proportion of returned farmland is only 2.55%, but all are suitable for forest growth. ③ The minimum data method, in theory, can provide a relatively efficient and economic compensation standard. The current policy standard of 7500 yuan/hm² is in the reasonable range of compensation. These results can provide scientific guidance for improving ecological compensation mechanisms and ecological compensation efficiency in the middle reaches of Heihe River.