The belt filter machine purifies liquids by allowing gravity to pass the liquid through a filter cloth, separating impurities. The drive mechanism's chain and mesh create a liquid pool depth, with the filter cloth laid over them. During operation, impure liquid carrying impurities flows to the non-woven fabric via a water-buffing device. The impurities are isolated by the filter cloth, forming a filter cake. As the filter cake thickens, the liquid level rises, triggering the float level controller to send a signal. The reducer then starts, pulling the filter cloth, and the impurities and soiled cloth fall into a waste paper box, automatically replacing the filter cloth. After the filter cloth is replaced, the liquid level drops, the reducer stops rotating, and the machine proceeds to the next filtration cycle. The purified liquid is then transported to the main unit by a pump.