The　approximate　full-stress　design　method　associated　with　the　relative　difference　quotient　method,　a　2-level　optimization　algorithm　was　presented　for　structural　optimum　design　with　discrete　variables,　which　overcame　that　the　imitative　full-stress　design　method　could　not　be　used　for　the　structural　optimum　design　with　discrete　variables,　and　improved　constringency　of　the　relative　difference　quotient　method　greatly.　The　structural　optimum　design　with　discrete　variables　under　stress　and　section　size　constraints　can　be　directly　calculated;　and　the　structural　discrete　optimization　with　multi-loading,　multi-variable　and　multi-constraint　(including　dis-aplacement　constraints)　can　also　be　dealt　with　by　this　method.　A　relevant　computer　program　was　developed　for　the　method.　The　method　was　illustrated　by　two　numerical　examples.　The　results　of　the　examples　showed　that　the　algorithm　was　efficient.