Hydraulic hoses are usually used in servo or proportional systems like automatic gauge control(AGC), automatic tension control(ATC) or bending roll system. The volume expansion coefficientβis the key parameter for modeling and plays an important role in modeling precision. However,βis always selected between 70 MPa～350MPa by experience, and its accuracy can＇t be guaranteed. In the light of such problem, the mathematical model of β is first derived using displacement method. Then, a detection method for β of hydraulic hose is designed. A sealed cavity consisting of a plunger cylinder and hydraulic hose is filled with hydraulic oil for tests. The hydraulic oil in the sealed cavity is compressed and the hydraulic hose is swelled when the plunger cylinder is promoted by a loading system. The volume and the internal pressure are detected. The precise value of β is finally obtained by theoretical calculation. It is the proposed method lays the foundation for the high precision modeling of hydraulic hose.