The invention discloses a total reflection optical system, which comprises a condenser lens and at least one annular lens. The condenser lens has a first light incidence surface, a first light emergence surface opposite to the first light incidence surface, and a side surface connected between the first light incidence surface and the first light emergence surface. The annular lens comprises an annular main body and a protruded part. The annular main body encircles the condenser lens along the side surface and has an inner annular surface which faces the side surface, an outer annular surfaceopposite to the inner annular surface, and a total reflection surface abutted against the outer annular surface. The protruded part is abutted between the total reflection surface and the inner annular surface and completely protruded out of the inner annular surface.