An interference lens and a projection ambient lamp are provided. The interference lens includes: an interference sheet with a first surface and a second surface opposite to the first surface, the first surface being a rough surface; and a reflective film provided at the interference sheet; wherein light is reflected by the reflective film to form an interference pattern. The projection ambient lamp includes the foregoing interference lens, a light source and a focusing lens; light emitted from the light source passes through the interference lens and is reflected by the reflective film to form an interference pattern, which is focused by the focusing lens and projected on a medium. The present disclosure realizes simplification of the structure by providing a reflective film at the interference lens, hence utilization of light energy is higher, power consumption is lower, manufacturing cost is lower, and projection effect is better.