Based on the conventional structural optimal theory andconsidering the uncertainties of structural parameters, we present robustoptimal method for structures using non-probabilistic convex set theory. Wemodel the uncertain parameters which exist in the object function andconstraint conditions as convex set, and need not know their detailedstatistical information bur bounds of uncertainties. The proposed method canendure the variation of structural performance resulting from the variationof uncertain parameters. According to the variation range of them, we candetermine the range or interval of optimal solution. In this sense, theoptimal solution is one domain rather than a point. Numerical example often-bar truss is used to illustrate the method using non-probabilisticrobust optimization, which shows both the feasibility and superioritycompared with conventional methods.