Based on the topology optimization of truss,the genetic algorithm(GA) was improved more efficient.In the design of size and topological structure of the truss,binary encoding,crossover and mutation for size and topology variables were adopted separately and the initial solution was gained,with the accuracy of the size variable coding properly reduced to speed up the convergence of the GA.In order to prevent trapping in local optimal solution,a portion of initial solution was added to the new parents,and then the size of section was recoded and the final solution was searched in a better precision.Examples show that the method is effective to the topology optimization design of truss structures with discrete variables.