A significant portion of defense projects are complex projects. Uncertainty and complexity are important and intrinsic features of these types of projects that increase their time and cost and some have pointed to the ever-increasing relationship between these concepts. Different approaches have been proposed, such as the development and deepening of the intrinsic capability to overcome the undesirable effects of these properties. In this study, uncertainty, complexity and capability are examined in a range of complex product development projects. At first, using the literature of the subject, referring to the experts and applying the three-stage Delphi method, the components of each of these three concepts were explained. Also, the distribution of questionnaires among managers and experts of defense industry, the importance of factors and performance of defense industries in management and improvement of these factors were evaluated and identified by means of significance-performance analysis, status of factors and priorities of improvement. The findings of this study indicate that organizations associated with complex defense product development projects in the areas of uncertainty, complexity, and capability should focus on the weaknesses of the organization's dominant culture, ambiguity in goals, changes in estimates, environmental factors, technical complexities, goals, project nature, Focus on the environment and knowledge management capabilities, value management, large-scale project management, and innovative capabilities that are higher priority than other factors.