The process of studying the complexity factors associated with the theory of complexity is one of the required study and it is importance in the construction sector in Iraq. The Complexity Theory can be understood as the study of how order and pattern emerge from chaotic systems, conversely, how complex structures and behaviors emerge from simple rules. The complexity cognizes us how to contemplate about the development process. This paper introduces a brief outcome through identification complexity factor and review the previous studies to obtain the technical outcomes about the complexity theory. The studying complexity factors related with construction projects as be part to cover complexity thinking in construction project. The results of this study show that viewing of all these areas related to the complexity of the project and how it can help the management departments in construction projects in Iraq to understanding the complexity level of their project to put best construction management plans. Many engineers and experts participated in the presentation of the study outputs, and by drawing on their opinions to participate in the closed questionnaire. The participants were (engineers in construction sites, academics, engineering management experts, and technicians with direct relationship to construction projects). Based on the frequency analysis aspect, the order of the influencing factors was reached according to its rating from (poor to strong) which reflects the conclusions associated with the study. The importance of studying these factors on knowing the degree of complexity in construction projects and developing appropriate methodology for managing them.