This study deals with bottleneck detection with simulation techniques and time study. Modeling and simulation are potential tools for analyzing assembly lines such as clothing in a garment. Thus, the researchers attempted to experiment 160 numbers of replication in the arena tool. The experiment monitors the assembly process resources without altering the actual production scheme. In this study, the arena software and POM dedicated to modeling and measuring the performance of the existing Ronny t-shirt sewing line. The t-shirt is formed and has 12 main parts are assembled. For each activity, the researchers took 15 sampling observations using stopwatch. All the collected data are statistically analyzed using the input analyzer in arena for statistical significance and the expression resolution to be used for the simulation model. This simulation model has considered production resources like four threads over lock machines, single needle, two flat lock needles, machine operators, quality checkers, trimmer, batch arrival time Inter lot of pieces, sequence pieces, testing Different scenarios.