The invention discloses a long-wave infrared continuous zoom lens comprising a first lens group with positive diopter, a second lens group with negative diopter, a third lens group with positive diopter and a fourth lens group with positive diopter, wherein the first lens group is a fixed group and is formed by a falcate germanium lens with a convex surface which faces to an object side, and a magnification group which can change a system focus is formed by the second lens group and the third lens group; wherein the second lens group comprises a plano-concave zinc selenide negative lens with a concave surface which faces to the object side and a concavoconcave germanium lens; the third lens group comprises a falcate germanium lens with a concave surface which faces to the object side; thefourth lens group is a focus group which comprises a falcate germanium lens with a concave surface which faces to the object side; the focus of the zoom lens is F, the focus of the first lens group is F1, and the F/F1 is larger than 0.25 and is smaller than 0.75. The long-wave infrared continuous zoom lens has simpler structure, is easy to manufacture and process and can effectively reduce production cost.