Abstract By carefully analyzing the latest composition-dependent parameters of SiGeSn alloys, we come to realize that this system could provide type-II energy band alignment at direct bandgap condition. The discovery inspires us to explore the mid-infrared interband cascade laser (ICL) in SiGeSn system. Based on the eight-band k ⋅ p model, we theoretically design three schemes of ICL, in which the active region and the carrier injectors are optimized simultaneously. Afterward, the properties of TE-mode optical gain spectrums and differential gain are investigated individually for each scheme. Furthermore, the spontaneous emission spectrums and radiative current density are also calculated. Our theoretical results indicate that the active region composed of double-electron and triple-hole quantum wells has the best gain performance, reaching 660 cm⁻¹ for a single period of the ICL under 7.8 × 10¹⁸ cm⁻³ injected electron density. This work opens up another type of infrared lasers that can be developed from the group-IV system, offering a new pathway to achieving the monolithic integration in Si photonics.