The present invention discloses a low-F-number full-HD (high definition) projection lens comprising a lens assembly arranged between a projection surface and a DMD chip. The lens assembly comprises afirst negative meniscus lens, a second negative meniscus lens, a biconcave lens, a first convex lens, a second convex lens, a triplet lens, a third convex lens and a fourth convex lens orderly arranged in a same optical axis from left to right. Projection signal light modulated by the DMD chip is projected into a full-HD projection lens, and the projection signal light sequentially passes throughthe fourth convex lens, the third convex lens, the triplet lens, the second convex lens, the first convex lens, the biconcave lens, the second negative meniscus lens and the first negative meniscus lens to be imaged on a projection screen. The structure is simple, with a lens with a similar structure of a retrofocus lens with negative lenses in the front and positive lenses in the back as an initial structure, the size of the chip is changed, the design is optimized through changing and increasing and decreasing glass materials and scaling a focal length, finally a low F number is realized, and the picture clarity is ensured.