The invention belongs to the technical field of electric-power equipment detection, and in particular, relates to a detection device of dissolved gases in transformer oil based on infrared spectrum absorption. The device includes a light source system unit, a sensing arrangement unit and a detection acquisition and analysis unit; the light source system unit is composed of a high-power supercontinuum broadband light source, a light source controller and a photoswitch and is used for realizing output multiplexing control of the light source; the sensing arrangement unit is formed by arranging one sensing path of fiber Bragg grating hydrogen sensor series-connection wavelength division multiplexing and the other one sensing path of hollow photonic crystal optical fiber internal spectrum absorption sensing in a cavity body of an oil-immersed power transformer; the detection acquisition and analysis unit is composed of a wavelength demodulation device, a light intensity detector and a data acquisition and analysis device, the wavelength offset and the spectral absorption intensity of fiber Bragg grating hydrogen sensors are detected, and the data acquisition and analysis device records data and types and contents of corresponding fault gases are obtained by calculation; and on the basis, insulation conditions of the transformer oil are evaluated, positioned, analyzed and forecasted.