The objective of this study was to realize the free swimming of the crawl stroke with the previously developed swimming humanoid robot. The upper body of the robot was remodeled to fit a free swimming test. The developed robot was simulated to raise feasibility of the crawl stroke. Through the simulation, two improved models were proposed. In the experiment, the swimming humanoid robot was fitted to the two simulation models and both realized the crawl stroke successfully. The measured roll angle was about ± 60 degrees and the swimming speed was between 0.2 m/s and 0.24 m/s.