This research aims to build an integrated framework to analyze the production flow efficiency (in terms of worker utilization) of the manual machine component assembly process. Problems related to spontaneous decision making among the workers in the manual assembly processes which cause inconsistency in the manufacturing speed, productivity, and quality. Often it is difficult to simulate all the possible situations to reduce such inconsistencies. This study aims to suggest an alternative way by introducing a prediction framework that is integrated with Modeling and Simulation (M&S) and a CART algorithm. M&S is used to create different scenarios out of the original layout for comparison. The CART algorithm is utilized to extract decision rules from the simulation results. These decision rules provide an understanding of patterns that affect workers’ utilization rate. The research goal is to adopt the rules on the simulation models, and to offer guidelines on improved alternatives for building simulation models of manual assembly process.