Abstract: To make the most of productive potential of climatic resources is an effective way to raise the yield of agricultural crops. The present paper applied the method of Leith's to estimate the agroclimatic productivity of Hainan Island. It was indicated that the light, heat and water resources are abundant and the climatic yield of plants are high too in Hainan Is-land. Thus, the potential of crop yield per unit can increase to more than two times as much as present level. However, water is the principal limited factor on the agricultural production of Hainan Island. If the maximum climatic yield is to be achieved irrigation is needed to supplement the deficiency of water in the whole Island, especially the western and southern parts. It needs, on an average, 1778 tons of water per hectare in the whole Island.