An infrared laser zoom beam expanding system, applied to the field of laser processing, and comprising a first lens, a second lens and a third lens. The first lens and the third lens are plane-convex plus lenses, and the second lens is a meniscus minus lens. The first lens, the second lens and the third lens respectively comprise a first surface and a second surface, a third surface and a fourth surface as well as a fifth surface and a sixth surface. The radiuses of curvature of the first to sixth surfaces are ∞, −27, 10, 1.7, ∞, −103. The center thickness of the first to third lenses is 2, 1, 4. The outer diameters of the first to third lenses are 10, 3, 34. Proportions of the refractive indexes to the Abbe numbers of the first to third lenses are 1.8:25, 1.48:68, and 1.8:25. A distance between the second surface and the third surface is 10-27. An distance between the fourth surface and the fifth surface is 119-125, The unit is millimeter, and a tolerance is 5%. The system may perform beam expanding on entering light by 2-16 times, which may be adaptable to laser devices with different emergent diameters and divergence angles, and improve efficiency and accuracy of laser processing.