Abstract: The flax fiber reinforced epoxy resin composite was prepared by the vacuum assisted resin transfer molding (VARTM) process,the effect of volume fraction of the fiber on tensile strength was studied.Kelly-Tyson tensile strength prediction model was modified and thus built a new tensile strength prediction model of the composite,and the prediction accuracy of the model was calculated.The results show that the tensile strength of the composite reached a peak (63.10 MPa) when the volume fraction of the fiber was 38.6%.The critical length of the fiber,the tensile strength and the fiber length effect factor were different because of the different shear strength.The prediction accuracy of the tensile strength prediction model was 97.8%.