The objective of this study was to develop a musculoskeletal simulation for a swimmer wearing competitive swimwear. For the simulation, the body geometry and joint motion were put into the swimming human simulation model SWUM in order to calculate the distributed fluid forces acting on the whole swimmer's body. The distributed fluid forces were put into the musculoskeletal model. In addition to the fluid forces, the forces induced by the tension of the swimwear were also considered. As an example, the simulation for the crawl stroke was conducted. The results showed the time-varying effect of the swimwear on the muscle activity during swimming.