In DNA based computation and DNA nanotechnology, the design of good DNA sequences has turned out to be an essential problem and one of the most practical and important research topics. Basically, DNA sequence design problem is multi objectives problem, and it can be evaluated using four objective functions, namely, Hmeasure, similarity, continuity, and hairpin. In this paper, this problem is converted into single objective problem, where the weight of each objective is determined systematically using conventional weighted aggregation (CWA). Particle swarm optimization (PSO) is proposed to minimize those objective functions, subjected to two constraints: melting temperature and GCcontent. A model is presented in order to solve DNA sequence design problem based on PSO. To assess the utilization of CWA in the problem, the comparison between CWA and user-defined weights and other existing approach are demonstrated. The implementation of the optimization process is presented using 20 particles and the average values for 20 runs are shown.