To get low-risk design project of complex weapon equipment, the integrated design methodology based-on reliability is proposed. The product's reliability must be analyzed and quantified during the whole product life-cycle; and in the design phase, some measures must be taken to assure appropriate margin of the product during the service and mission environments.It is an important problem to find one balanceable optimal design amid advantage, reliability and robustness of the product, so that these characteristics are all brewed and produced during the design procedure, and not analyzed and evaluated afterwards. Due to product design and decision-making with incomplete information in general, the new methodology of quantification of margins and uncertainty (QMU) is introduced based on traditional decision-making methodology, which does depend on experiment results and partial numeric simulations, to provide an engineering analysis method of validity evaluation. Some practice suggested that this design methodology may have extensive engineering application future.