How to determine ecological compensation standard is one of the main difficulties during designing the ecological compensation scheme. Taking the central mountainous area of Hainan Island as a case study, we calculate the cash flows of rubber and betel based on remote sensing interpretation, survey and interview. And the opportunity cost of ecological forest protection was determined (2.37×108 Yuan RMB/year) in the central mountainous area, which was considered the ecological compensation standard. Moreover, the impacts of time factor and risk factor have on opportunity cost were discussed: time factor could be divided into discount rate and cash flow in different periods, risk could reduce the opportunity cost. The results suggest that to combine opportunity cost calculation with farmland ownership is a suitable method to determine the ecological compensation standard, and considering the impacts of time factor and risk factor will make the estimation of ecological compensation standard more reasonable.