An exemplary projection lens system includes, in order from the magnification side to the reduction side thereof, a first lens with negative refraction power, a second lens with positive refraction power, a third lens with negative refraction power, and a fourth lens with positive refraction power. The projection lens system satisfies the formulae 3.7 1.41; where TT is a total length of the projection lens, f is an effective focal length of the projection lens system and BFL is a back focal length of the projection lens system.