An optical lens includes a first lens (L1), a second lens (L2), a third lens (L3), and a fourth lens (L4), which are successively coaxially arranged along the transmission direction of incident light, wherein the first lens (L1) and the fourth lens (L4) are negative meniscus lenses, the second lens (L2) is a positive meniscus lens, and the third lens (L3) is a positive plano-convex lens. The optical lens can be applied to an optical system of a laser processing device, when a utilized processing wavelength is different from a monitoring wavelength, the imaging chromatic aberration in a monitoring system may be eliminated, particularly when a wavelength of the far infrared region is utilized as a wavelength for laser processing. When using the red light wavelength as the monitoring wavelength, the monitoring system can achieve a better imaging effect, thus ensuring the quality of laser processing.