The invention relates to a recoil mechanism for a light mortar, and belongs to the technical field of military equipment. The recoil mechanism for the light mortar comprises an outer barrel, a middle partition plate, a first piston plate, a connecting rod, a buffer solution, a second piston plate and a pressure regulating spring, wherein air vents and a mortar pestle are arranged at the bottom of the outer barrel, and the atmospheric pressure maintains balanced; the first piston plate and the second piston plate are mounted at the lower part of an inner cavity of the outer barrel; the pressure regulating spring is arranged between the second piston plate and the bottom of the inner cavity of the outer barrel; the cavity between the middle partition plate and the second piston plate is filled with the buffer solution; a plurality of liquid-permeable holes are formed in the first piston plate; the middle partition plate and the connecting rod are arranged between the first piston plate and the bottom of a launching tube; and an upper opening of the outer barrel sleeves the middle lower part of the launching tube. According to the recoil mechanism for the light mortar, a part of recoil kinetic energy can be buffered and consumed, the impact on a seat plate is reduced, and the continuous launching speed and fighting ability of the mortar are improved.