Projection system and AR projection device

The invention provides a projection system and an AR projection device. The projection system sequentially comprises a diaphragm, a first optical prism, a lens group and an imaging module from an object side to an image side, the first optical prism comprises two transmission surfaces and two reflection surfaces, the optical axis of the object side surface of the first optical prism does not coincide with the optical axis of the image side surface of the first optical prism, and the object side surface of the first optical prism is a convex surface; the diaphragm and the object side surface of the first optical prism are positioned on the same optical axis, and the image side surface of the first optical prism, the lens group and the imaging module are positioned on the other optical axis; according to the projection system, the length TTL from the diaphragm to the image source surface on the Z axis, the vertical distance THL between the optical axis on the diaphragm and the optical axis of the lens group on