The invention discloses an enzymolysis-membrane filtration circulating device and a method for preparing shellfish polypeptides by the same. The enzymolysis-membrane filtration circulating device comprises a raw material tank, a first thermostatic bath, an enzymolysis tank, a second thermostatic bath, a centrifugal device, a membrane filtration assembly, a liquid collecting tank, a feed pump, a first circulating pump and a second circulating pump. The method for preparing shellfish polypeptides by the device comprises steps of pretreatment of raw materials, hydrolysis of mixed enzyme, enzyme deactivation, centrifugation and filtration, membrane filtration and the like. The device can simultaneously and continuously perform hydrolysis of mixed enzyme and membrane filtration and perform enzymolysis again on intercepted ultrafiltrates with large molecular weight, the raw materials are saved, and the utilization rate of the raw materials and the production efficiency of the products are increased. The shellfish polypeptide products prepared by the method have good quality, a large quantity of short polypeptides can be produced, the yield of the shellfish polypeptides can reach 90% or above, meanwhile, the conversion rate of the prepared shellfish polypeptides can be effectively increased to 85% or above, and the inhibition rate of the shellfish polypeptides can be increased to 95%or above.