Evolutionary algorithm have been shown to be very effective optimization tools for a number of engincering problems and specially pratical optimization problems. the use of nonlinear finite element can asist greatly in achieving a safe design. however, commercially available finite element programs are not designed for optimization tools. design feature which included in commercial structure analysis program usually used to check if the member pass the code or not. 'home-written' structure analysis program can be designed to achieve this task. however it may suffer from serious drawbacks such as bugs, lack of user friendliness, lack of generality,and umproven reliability. a new approach is presented for the optimization of steel truss by combing evolutionary algorithms and commercial sructure analysis program. the purpose of this approach is to create a program which combine SAP2000 structure analysis program with evolutionary algorithm for optimizing truss structure. strategies are discussed to model the choromosome and to code evolutionary to handle such constraints. member grouping is created for reducing the search space. the implemented process is tested on 10 members of 2D steel sructure, 25 members of 3D steel structures and 36 memebrs of 3D steel sructure, where the results are compored with previous researches. because of data size and number population, parallel computing method used in this paper. it is concluded that this method can server as a very usefull tool in enginering design and optimization.