Abstract: Glass fiber fabric (5HS)/epoxy resin E51 prepreg was prepared to study the applicability of on-line resin pressure measuring system during autoclave process in this paper. The effect of viscosity on the dynamic response properties was analyzed. In addition, the resin pressures inside flat, tapered and L-shaped prepreg stacks under zero-bleeding condition were measured by this system and calculated from theoretical model, respectively. These experimental data were additionally compared with theoretical ones to assess its accuracy. The results show that the viscosity greatly influences the dynamic response of the system. As the viscosity of resin is less than 25 Pa·s, the high dynamic response can meet the requirements of resin pressure measurement inside composites. In addition, the measured resin pressures inside prepreg stacks with different shapes involved in this paper are consistent with the theoretical ones. As the autoclave pressure reaches to 0.5 MPa, the relative errors are approximately 2%, and the accuracy of the system is validated.