The present disclosure relates to the field of automobile lamp technologies, and in particular, to a light source module based on a graded index lens, a lamp assembly including the light source module, and an automobile including the lamp assembly. The light source module includes a light source and a graded index lens disposed in front of the light source. Light emitted from the light source is incident to an incident surface of the graded index lens, and is emitted from an out-light surface of the graded index lens after being refracted and converged by using the graded index lens. The graded index lens converges the light emitted from the light source, so that the light has relatively large optical radioactive energy and a relatively small divergence angle on the out-light surface of the graded index lens.