The invention discloses a device and method for measuring a refractive index of an intermediate infrared multi-wavelength material. The device comprises a laser diode, a beam shaping device, an input mirror, a laser crystal, a spherical surface high reflection mirror, a prism pair, a slit, an output coupling mirror, a Faraday isolator, a half-transparent and half-reflecting mirror, an adjustable diaphragm, a precise rotating platform, a spectrograph and a dual-channel power meter. The invention realizes direct measurement of refractive indexes of a material to be measured in a wide-spectrum range under different intermediate infrared wavelengths, solves the problem of difficulty in measurement of the refractive index of the material with intermediate infrared wavelength, and is simple andeasy in a measurement process, thus the measurement process of the refractive index is greatly simplified and the measurement cost is reduced.