Abstract: Among the advanced composites reinforced by high-performance fibers,the plastic reinforced by short carbon fibers is remarkable by its variety of performance and lower cost.By synthesizing the preceding productions,the strength rule of mixture of short fiber reinforced composite is educed,and the modified formula is obtained by using the length coefficient to correct the asymmetry of stress distribution in material.The math model is established to estimate the influence disciplinarian on strength of parameters.By taking carbon fiber reinforced PTFE composite as the example,the strength forecast method is explained,and it will provide the reference to new material usage and new structure design.