Variation Orders is often a reason for construction projects exceeding projects budget and delays; it is a global problem, particularly intensive in the case of a recession of the local economy and stagnation. In Iraq, all the projects have delays in completion, and the cost affects because of the variation orders, which are not well managed. The objective of this study was to identify the key causes responsible for the variation order in construction projects in Iraq using the system dynamic. System's dynamics is the discipline of academics and rooted initially been in management and the engineering sciences. The data relating to the performance of construction projects from 27 projects adopted by Diyala University were collected. Personal interviews and questionnaires survey to the selected projects of specialized engineers were done. The results revealed that the size of variation orders in Iraqi construction projects was high, and 13 key causative factors led to variation orders. The variation in cost was the most influential factor effecting the construction project in Iraq.  When variation orders in a cost increased, the owner's opinion decreased. When the external factors increased, cost variation orders increased. It was concluded that minimizing the variation orders was very important to realize the cost in the construction projects. Therefore, the authority management and project managers must make a plan to address these key causes in future projects to ensure their success