The mechanism of the non-agricultural transfer of rural labor to agricultural production efficiency and their interrelationships is a problem worthy of further discussion at this stage in China. The mediating effect model is constructed, the least square method is used for regression, and the instrumental variable method is used to solve the possible endogeneity problem. Through the investigation of farmers in Loess Plateau region, this paper analyzes the effects of factor substitution and planting structure adjustment after agricultural labors work outside and its impact on agricultural land output from the theoretical and empirical aspects, as well as the impact of off-farm employment on agricultural land output under different constraints. Results showed that the negative influence of labor non-agricultural transfer on farmland land output rate is - 7.264, and farmers' participation in returning farmland to forests can alleviate the negative impact of non-agricultural transfer on the agricultural land output. Labor substitution factor investment plays a part in the mediating effect, and part of the mediating effect is - 0.879. The adjustment of agricultural planting structure plays the whole mediating effect, that is to say, the larger the scale of labor non-agricultural transfer in Loess Plateau area, the more unfavorable for farmers to invest in labor substitution agricultural factors of production, and the more they are inclined to grow food crops. When the constraint conditions of factor substitution difficulty and planting structure adjustment space are considered, the higher the factor substitution difficulty is, the smaller the planting structure adjustment space; the negative effect of the non-agricultural transfer of labor on the agricultural land output rate is more obvious. It provides effective reference value to judge the development stage and trend of regional agriculture and puts forward relevant policy suggestions to guarantee the development of regional agriculture and farmers' life.
Keywords: Agricultural land output-rate; Factor input structure; Forest area; Labor non-agricultural transfer; Loess Plateau; Planting structure constraints.