The invention provides a zoom lens which comprises a first lens set with a positive focal power, a second lens set with a negative focal power and a third lens set with a positive focal power sequentially from an object side to an image side, wherein the position of the first lens set is fixed; the second lens set is a zoom lens set; when a zoom lens zooms from a wide angle end to a telescopic end, the second lens set moves towards the object side; and the position of the third lens set is fixed and used for regulating the position of an imaging surface. The zoom lens has the advantages of small volume and simple structure.