The invention discloses a high-sensitivity multi-reflection optical absorbing device which comprises a reflection optical cavity, end covers, an intermediate infrared LED (Light Emitting Diode) light source and two photodiodes, wherein the end covers are connected to the upper end and the lower end of the reflection optical cavity in a sealing manner, an air inlet and an air outlet are respectively formed in the upper end cover and the lower end cover; the reflection optical cavity is a stainless steel cylindrical member, the inner wall of the reflection optical cavity is a diffuse reflection surface formed by gold plating after coarse grinding, the reflection optical cavity is provided with an optical inlet and two optical outlets along the axial direction of the side wall, the intermediate infrared LED light source is arranged in the optical inlet, and the photodiodes are arranged in the optical outlets. The high-sensitivity multi-reflection optical absorbing device is capable of effectively prolonging the length of a detection optical distance within a smaller space, has the characteristics of compact structure, convenience in regulation, stable light path, small influence by environment temperature, high sensitivity and detection precision, and the like, and is especially suitable for measuring concentration of hydrocarbon explosion gases in a ship cabin environment.