A starry sky projection apparatus relates to the technical field of projection lamps, comprising a starry sky lamp body, wherein the starry sky lamp body is provided with a base and a housing, and a projection lamp assembly is disposed in the housing, and the projection lamp assembly comprises: a gobo mapper, wherein the gobo mapper is provided with a slot, and the housing is provided with a replacement slot on one side adjacent to the slot, and the slot is for a user to insert different gobos through the replacement slot. An optical lens is detachably provided on the housing. The optical lens is provided with a plurality of different mirror surfaces, and the plurality of optical lenses can be replaced by the user to display a variety of different nebulae.