Abstract: Disclosed is a light effect projection device, including a control unit, a condensing diffraction assembly and a first lamp source, wherein the first lamp source and the control unit are both fixed in a housing, the first lamp source is electrically connected to the control unit, the condensing diffraction assembly is located above the first lamp source, the condensing diffraction assembly at least includes a plastic condensing lens, the condensing lens is shaped like a spherical crown or a semi-sphere, an incident plane of the condensing lens is concave, and the incident plane or an emergent plane of the condensing lens is of a polyhedral structure; further including a driving unit which is fixedly arranged in the housing and electrically connected to the control unit, wherein one part of the condensing diffraction assembly is fixed at a power output end of the driving unit for driving connection.