Sr3Sn2O7:Sm3+ is a widely studied mechanoluminescent material, but there is still a lack of research on the doping amount of Sm3+. In this paper, Sr3-xSn2O7: xSm3+ was prepared by a high-temperature solid-state method. A sample of Sr3Sn2O7 with a small amount of Sm3+still maintains a non-centrosymmetric double perovskite structure. The sample prepared has a stable photoluminescence, a long afterglow and mechanoluminescence after UV excitation or load application. The mechanoluminescence originates from the electron transition from the 4G5/2 excited state of Sm3+ to the 6HJ (J=5/2, 7/2, 9/2) ground state. The luminescence performance was optimized by adjusting the value of x, and the optimum performance was achieved when x = 0.020. This study can provide a guidance for the future related research.