The invention provides a donkey-hide gelatin cake online water monitoring system and a method thereof. The system comprises a first water monitoring unit arranged on a sweet gelatin pipeline, a secondwater monitoring unit arranged in a jacketed pan, and a third water monitoring unit arranged on a donkey-hide gelatin cake conveyor belt. Through the first water monitoring unit, the second water monitoring unit, and the third water monitoring unit, the water is monitored in real time by the online water monitoring system during the production process. The production process can be better controlled, and the production efficiency and donkey-hide gelatin cake quality are improved. The online water monitoring method is simple and easy to do and can accurately measure the water content of a donkey-hide gelatin cake in time.