The invention discloses a measurement device and a measurement method for annular gap flow of a plunger-copper-sleeve pair, wherein the measurement device and the measurement method belong to the field of hydraulic equipment detecting technology. The measurement device comprises a body part, an oil supplying device and a collection measurement device, wherein the body part is used for fixing a copper sleeve test piece and a plunger test piece. The oil supplying device is used for supplying hydraulic oil with stable pressure. The collection measurement device is used for acquiring test data. The measurement device has advantages of simple operation and convenient control. Through changing oil supplying pressure and hydraulic oil temperature and changing the plunger test piece and the copper sleeve test piece, influences of different oil supplying pressures, different hydraulic oil temperatures, different surface characteristics and different slit heights to sealing tightness and lubricity of the plunger-copper-sleeve pair are researched.