Human and his performance is a vital factor in protection of asset including environmental properties. The objective of this study was to evaluate the impact of total system design factors (TSD) on human performance in a power plant. The TSD factors are defined as design factors, which have impact on overall performance of the power plants in context of total human engineering or macroergonomics. The systems being studied are the control rooms and maintenance departments of a 2000 MW thermal power plant. To achieve the above objective, the TSD factors were addressed and assessed through a detailed questionnaire. The relationships between TSD factors and human performance were then examined through non-parametric correlation analysis (Kramer’s Phi) and Kruskal-Wallis test of means. The results of this study show that the macroergonomic factors such as organizational and safety procedures, teamwork, self-organization, job design and information exchange, influence human performance in the power plant. The findings also suggest that the selected macroergonomic factors are correlated to human performance and must be considered, designed and tested concurrently with the engineering factors at the design phase of the system developmental cycle. Consequently, total system’s faults and organizational errors are reduced to an acceptable level and human performance is significantly increased. The main goal in such program is customer"s satisfaction (Internal customers). However, more elaboration on the scientific tools for implementation of TDS factors in context of human performance is also under investigation.