The common feature of small-scale farmers is the diversification of production.However,specialization is the inevitable trend in the change of operational method in order to achieve comparative advantages and benefits.Farmer’s horizontal specialization is determined by farmer’s resource endowment,behavior ability and trading features of farmer’s participation in the division.This paper constructs the framework of “behavior ability-trading features——horizontal specialization degree” first and then measures the horizontal specialization from concentration of planting variety,concentration of planting scale and concentration of sales scale in accordance with the farmer’s sampling questionnaire and finally analyzes these influencing factors.The result shows that the basic elements of agricultural production,such as water resources,labor resources etc are the important elements affecting the specialization,while flat land and thicket of land are the basic conditions of specialized operation.The farmer’s disposal ability has great influence on horizontal specialization,while trading scale and trading risk have no obvious influence.