Short-wavelength red laser is a new wavelength light source that is urgently needed to be developed for laser display and biomedical applications. In this paper, a red light semiconductor laser with a wavelength of 620 nm has been designed and simulated based on a Ge/Si_xGe_1-x substrate. The laser uses a Ge substrate and a Si_xGe_1-x substrate layer. By changing the Si mole fraction in the Si_xGe_1-x layer, the lattice constant of each layer of the AlGaInP materials in the laser structure is adjusted to achieve a GaInP quantum well with a high Ga mole fraction and shorten the laser wavelength of the GaInP quantum well to 620 nm. By calculating the physical parameters of SiGe and AlGaInP materials, the influence law of GaInP quantum well active region structure and Si_xGe_1-x substrate layer components on the output characteristics is studied, and the structural parameters of the laser are optimized. The simulation results show that the laser designed at 298 K temperature has an output wavelength of 620 nm, a threshold current of 0.58 A, an output power of 1.20 W, and a conversion efficiency of 38.3%.