The Systems Engineering design process is challenged to deliver successful complex systems in multidisciplinary and heterogeneous components. Growing human needs and evolving society bring ever greater challenges in the formation of a complex and large engineered system. System complexity is related to lots of parts and large size of the system when there is difficulty in understanding how the system works or in predicting the consequences of any change that may affect the process and systems develop itself. The leadership is performing an important role to manage a complex system. Leaders should be able to set back from immediate focus and look at the desired big picture. In practice, many factors contribute to Systems Engineering complexity in this review. This study intends to explore and analyze the complexities and the factors that contribute to the complexity of the Systems Engineering design approach. The data in this study were collected systematically from several electronic scholarly databases, including the ISI Web of Science, Scopus, Wiley Online Library. This study quantified the challenges and causes of the Systems Engineer complexity. Then, the challenges were categorized into two groups, managerial and technical causes. Ultimately, seven Systems Engineering complexity factors were identified, and their impact on the Systems Engineering processes was ranked using the Pareto principle. Among the factors, rapidly emerging technology was the most significant factor contributing to Systems Engineering complexity.