The invention discloses a projection lens which comprising a front group of lenses, a back group of lenses and a diaphragm arranged between the front lens and the back lens. The front group of lenses includes a first lens, a second lens and a third lens which are sequentially arranged, and most refracting surfaces of which are bent towards the diaphragm, wherein, the second lens and the third lens form a front balsaming lens. The back group of lenses includes a fourth lens and a fifth lens sequentially arranged, wherein, the convex surface of the fourth lens is bent towards the diaphragm which is positioned at the front focus of the back group of lenses. The interval between the third lens curved surface top close to the diaphragm and the diaphragm is less than the interval between the fourth lens curved surface top close to the diaphragm and the diaphragm. In the invention, the projecting lens formed by few lenses has simple structure, small size and low cost and also has little stray light and aberration, short projection distance and long back focal length, meeting the demand for minisize. In addition, the invention also provides a minisize projection optical engine using the projection lens.