The invention relates to a high-brightness ultra-wideband medium infrared super-continuum spectrum light source. A femtosecond optical parametric amplifier (OPA), a space coupling device and selenide optical fiber are sequentially arranged along a light path direction, the femtosecond OPA comprises a femtosecond mode locking Yb laser, a continuous tuning semiconductor laser, a one second wave plate, a two-tone beam splitter, an achromatic doublet lens, a temperature control device, a periodically poled lithium niobate crystal, an infrared lens and a long-wave germanium-through optical filter, the space coupling device comprises two pieces of infrared lens and a three-dimensional adjustment rack, the selenide optical fiber is arranged on the three-dimensional adjustment rack between the two pieces of infrared lens, and the three-dimensional adjustment rack is used for fixing the optical fiber. By the high-brightness ultra-wideband medium infrared super-continuum spectrum light source, medium infrared super-continuum spectrum output with average power more than 20mW, a spectral range covering 2 to 12 micrometers and high spectrum flatness can be acquired, and the brightness of the high-brightness ultra-wideband medium infrared super-continuum spectrum light source is improved than a synchrotron-radiation medium infrared light source by two orders of magnitude.