Based on the introduction of research theories about rural labor force transfer at home and abroad, taking Liaocheng City as the representative of medium and small cities, transfer situation of rural labor force in Liaocheng City is discussed from several aspects, including the transfer of total labor force, structure of labor force, flow of regional labor force, industry selection of labor force, and income of labor force. Combining with the situation of labor force transfer in Liaocheng City, social benefits, including both negative and positive benefits, of labor force transfer are analyzed. From the aspect of positive benefit, foreign labor is one of premier builders for in-flow area (city), fills in the structural lack of labor force, and has made huge contributions to urban construction. Meanwhile, for out-flow area (village), transfer of surplus labor force can reduce the employment pressure in rural areas, increase the income of peasant households, and promote the development of rural economy. From the aspect of negative benefit, a large number of labor forces pouring into cities will bring pressure on the transportation and infrastructure, increase the instability factor of city, and cause difficulties in the management of city. At the same time, a large number of young labor forces work in cities, leaving only the old and sick in rural areas. This might become a hidden danger to the development of agriculture. Push-Pull Theory is used to analyze the socio-economic factors affecting labor force transfer. Suggestions are put forward to reform the household registration system, to improve the cultural quality of rural labor force, to develop rural secondary and tertiary industries, to promote the rapid and harmonious development of economic society in underdeveloped regions, and to provide scientific reference for the sustainable development of regional economy and the construction of new socialist countryside in Liaocheng City.