The minimum weight design method of large-span statically determinate trusses satisfying the displacement constraint is studied. The displacement calculation formula is provided, and the critical condition of minimum weight design satisfying the condition of allowed displacement is educed using Cauchy inequality. The distribution coefficient, which is used to obtain the minimum weight design, is defined and the coefficient distribution method is proposed. An engineering example is analyzed using the coefficient distribution method above, and the compared results are discussed. Study results show that the proposed method, coefficient distribution method, is correct，reliable and effective.