Owing to their unique characteristic of direct mechanical-to-optical energy conversion, mechanoluminescence (ML) crystals have drawn considerable interest for visible stress sensing, flexible and stretchable displays, and advanced anti-counterfeiting. However, among the visible emissions of synthetic ML materials, high-performance red-emission semiconductors with ideal color-rendering indices are relatively scarce, which restricts their future applications. In this work, red ML emission with CIE coordinates  in Mn-doped ZnGa2S4 prepared by a molten salt shielding synthesis method in the air is reported. ZnGa2S4 has a cubic crystal structure composed of a layered [ZnS4] tetrahedral unit that plays an important role in efficient ML. Based on density functional theory calculations, the relationship between ML performance and crystal structure is revealed, which will help in the development of new high-quality ML materials. The Mn-doping of ZnGa2S4 causes a slight deformation of the crystal structure, leading to band bending and the formation of ML features in response to mechanical stimuli. The deep-red ML emission of the ZnGa2S4:Mn crystals prepared by this method holds great promise for advanced flexible and stable displays and force/pressure sensor applications.