The invention relates to a zoom lens. The zoom lens comprises a first lens group (A), a diaphragm (S) and a second lens group (B) which are sequentially arranged from the object side to the image sidealong the optical axis, wherein the first lens group (A) is a negative power lens group and is used for carrying out refocusing during zooming; and the second lens group (B) is a positive power lensgroup and is used for changing the focal length during the zooming. The glass-plastic composite zoom lens provided by the invention has the advantages that the field angle range covers the monitoringrange of a mainstream prime lens for security monitoring, the maximum aperture is smaller than or equal to 1.1, the focal length zoom ratio is larger than 4.0, co-focusing of visible lights and infrared lights can be achieved, and the resolution reaches 4K.