Abstract: This paper deals with the problem of minimum weight design for geometrically nonlinear truss structures subjected to constraints of stresses and displacements. An optimization algorithm based on optimality criterion suitable for geometrically nonlinear truss is presented. The formula used to calculate the displacement gradient of such truss is derived in detail. Moreover, a new method of approximate re-analysis for nonlinear structures is given. Application of the method to drilling mast and some other truss structures demonstrates the usculness and accuracy of the algorithm.