This article uses a new space-time model to analyze the space-time distribution of the Milky Way. The new space-time model can better explain the three-layer structure of the Milky Way. These three-layer structures are the kernel, the bulge and the disc. The analysis results show that the gravitational force of the galactic kernel’s substance can act on all the masses in it. The gravitational force generated by the bulge’s substance can only cover most of the masses in it, but the substance at the edge of the bulge cannot be covered. The density of matter on the disc is very low, which causes the galaxies in the low-density regions of the MW disc to basically move freely. The galaxies on the spiral arms will have a strong gravitational interaction. However, the new model has to explain why many galaxies can still maintain a disc-like structure when many galaxies are in free motion, and may need to use the concept of dark matter.