The invention discloses an on-board seepage flow and outflow concentration real-time monitoring device and method of a geotechnical centrifuge. The on-board seepage flow and outflow concentration real-time monitoring device comprises a measuring cylinder, a comparing cylinder, a conductivity electrode, a differential pressure transducer, a collection pipeline, and the like. The on-board seepage flow and outflow concentration real-time monitoring device is structurally characterized in that the measuring cylinder and the preparing cylinder are organic glass cylinders with the same inner diameter and height and opened upper ends; threaded holes are formed on the parts, adjacent to the bottom, of the side walls of the measuring cylinder and the comparing cylinder and both ends of the differential pressure transducer are connected by virtue of a soft pipe; the conductivity electrode is reversely installed on the bottom of the measuring cylinder; and the collection pipeline is introduced from the outflow hole of the downstream surface of an antifouling barrier model and extends downwards until to the bottom of the measuring cylinder. The on-board seepage flow and outflow concentration real-time monitoring device can be used for automatically monitoring the seepage flow leaked from the downstream surface of an antifouling barrier and the outflow concentration during the test in real time. The on-board seepage flow and outflow concentration real-time monitoring device can be used for a centrifugal model test of ionic contaminants for long-term migration in the antifouling barrier, and an effective tool is provided for research of long-term service performance of the antifouling barrier.