The potential grain productivities of corn,rice and soybean was respectively calculated by using mechanism method in major grain producing areas of Liaohe basin in Liaoning province.It was surveyed that in this region the total potential productivity of corn was 8 115 kg·hm-2,the total potential productivity of rice was 9 765 kg·hm-2,the total potential productivity of soybean was 3 375 kg·hm-2.Fertilizer production effect for corn，rice and soybean were 2 5993 kg·hm-2,2 5498 kg·hm-2 and 1 9022 kg·hm-2.The main crop yield limiting factors size were as follows:corn temperature>water>fertilizer>soil,rice temperature>fertilizer>soil>water,soybean fertilizer>temperature>water>soil.