Abstract: Advances in the soil fertility （including SOM and N，P，K） conservation functions of agro-forestry ecosystem and their assessment methods were summarized and key operational assessment principles proposed. The agro-forestry ecosystem function to conserve soil fertility in the two ways: i） natural soil fertility, including tree and crop residue, underground biome remaining in the soil; and ii）artificial chemical and organic fertilization of the soil. For assessment purposes, the functions were put into two categories－the flow-type eco-service（FE）, interpreted as enhancing soil fertility; and the storage-type eco-service（SE）, interpreted as sustaining soil fertility. The formulas and assessment parameters are inherently different for specific regions and sub-ecosystems. Using this approach, the soil fertility conservation function of Foshan agro-forestry ecosystem was assessed for year 2005; the FE value is estimated at 83.2 million yuan and SE value calculated at 1 982.8 million yuan.