Abstract: A hybrid algorithm for topology optimization of trusses with discrete variables is developed which combines relative difference quotient algorithm with chaos optimization. Taking advantage of the quick optimization of relative difference algorithm with discrete variables and ergodicity of chaos, the possibility of being trapped in a local optimum can be reduced significantly and topology optimization in the whole design space can be realized. In order to decrease the number of re-analysis, some auxiliary techniques, such as comparing with quasi-optimal solutions and identifying geometric stabilities, are adopted. Meanwhile, by introducing effective re-analysis method, the solving efficiency is improved and some difficulties in the process can also be avoided. Examples are presented to show the validity of the proposed method for topology optimization design of truss structures with discrete variables.