The magnetocaloric effect and phase transition properties of La_0.75Ce_0.25Fe_11.5-xAl_0.2Si_1.3Sn_x (x=0, 0.05, 0.1, 0.2, wt%) alloys were investigated. X-ray diffraction results show that with increasing the Sn doping content, the content of 1:13 main phase is decreased, and the content of α-Fe and LaFeSi phases is increased. By combining the density functional theory with experimental results, it is found that increasing the Sn doping content can increase the lattice constant and enhance the exchange interactions between adjacent atoms, thereby increasing the Curie temperature. When the magnetic field is 2 T, the maximum magnetic entropy change in the system is 13.59 J·kg^-1·K^-1 and its relative cooling power is 154 J/kg, showing great potential as magnetic refrigeration material. Based on the Banerjee criterion and the field dependence index n of isothermal entropy change, it is concluded that when the Sn doping content is 0.05wt%, the first-order phase transition changes to the second-order phase transition of the alloy. The phase transition behavior of the alloy is very sensitive to the Sn content, and multi-stage series refrigeration can be achieved by adjusting the doping content.