Abstract: Flax noil fibers reinforced polylactide composites were prepared by means of the non-woven method and hot pressing technology. The effects of volume fraction on tensile strength of the composites were discussed. Based on Kelly-Tyson tensile strength model and some related theories，a new model for predicting discontinuous natural fibers reinforced biodegradable composite (D-NFRBC) was proposed，which contains not only the effect of probability distributing features of the fibers strength，length，fibers tropism angle and diameter on the predicted strength，but also the effect of the rest ricted connection among the shear strength of the composite，the critical length of the fibers and the terminal tensile strength of the fibers in the composite on the strength. The results reveal that the tensile strengths reach a peak at the fiber volume fraction of 39.6%，and the predicted values calculated by the new model agree well with the experimental values.