This paper aimed to study the changing laws and differences of soil conservation functions of Pinus tabulaeformis forests with different densities in the loess area of western Shanxi Province, and to evaluate their soil conservation function, so as to strengthen forest stand management and ecological restoration. Four kinds of P. tabulaeformis plantations with different densities (925 plant/hm², 1 325 plant/hm², 1 750 plant/hm² and 2 250 plant/hm²) in the Caijiachuan watershed of Jixian County, Shanxi Province were taken as the research objects. The soil bulk density, porosity and other physical properties, organic matter and other chemical properties as well as the amount of slope runoff and sediment were measured and analyzed, and 12 evaluation indicators were determined, and the entropy weight method (EWM) was used to evaluate comprehensively the soil conservation functions of each P. tabulaeformis forests. The results showed that:(1) There were significant differences in soil bulk density, total porosity, non-capillary porosity, capillary porosity, total nitrogen, total phosphorus, ammonia nitrogen, nitrate nitrogen and available phosphorus among the four kinds of P. tabulaeformis plantation (P<0.05). (2) The change of stand density would change the 12 indicators of soil physical properties, soil nutrients and runoff and sediment volume of the P. tabulaeformis forest. Among them, soil bulk density, runoff and sediment volume all decreased first and then increased with the increasing of forest density. Soil organic matter, total nitrogen, total phosphorus, nitrate nitrogen and available phosphorus showed the opposite tendency with the increasing of forest density. (3) The soil physical structure, soil fertility, runoff and sediment yield of different P. tabulaeformis forests all showed certain change laws with the change of density. The improvement of soil structure and soil fertility increased first and then decreased with the increasing of forest density. With the increasing of forest density, the amount of runoff and sediment decreased first and then increased. (4) The evaluation of soil conversation function of P. tabulaeformis plantations with different densities showed that the soil conservation function of P. tabulaeformis forest increased firstly and then decreased with the increasing of density. The conservation soil function of P. tabulaeformis forest land with a density of 1 750 plant/hm² was relatively good. From the perspective of soil conservation, it was recommended that 1 750 plant/hm² should be used as the management density of P. tabulaeformis plantations in the loess area of western Shanxi. This density could better maintain water and soil and improve the soil quality of forest land.