Forest has a strongfunction in storing water, conserving soil and protecting farmland. In the study, based on fleld management and survey, these effects of forest in Beijing were determined and quantified. According to the principles and methodology of environment economics, the values of forest to conserve soil and water were accounted. The result shows that the total value of forest to conserve soil and water in Beijing is as much as 1129.58×10~8 yuan, in which the value of water storage is 1107.92×10~8 yuan, being 98.08% of the total. Forest has a strong function in storing water, conserving soil and protecting farmland. In the study, based on fleld management and survey, these effects of forest in Beijing were determined and quantified. According to the principles and methodology of environment economics, the values ​​of forest to conserve soil and water were accounted. The result shows that the total value of forest to conserve soil and water in Beijing is as much as 1129.58 × 10 ~ 8 yuan, in which the value of water storage is 1107.92 × 10 ~ 8 yuan, being 98.08% of the total.