Effects of the length ratio between the contractile element (CE) and the series elastic element (SEE) on the behavior of the muscle tendon complex were investigated during stretch-shortening cycles. A computer simulation model of the Hill-type muscle tendon complex was constructed. The proximal end of the CE was affixed to a point in the gravitational field, and a massless supporting object was affixed to the distal end of the SEE. A mass was held on the supporting object. Initially, the muscle tendon complex was fixed at a certain length, and the CE was activated at 100%. Through this process, the CE contracted as much as the SEE was stretched. Thereafter, the supporting object was released, which caused the muscle tendon complex to propel the mass upward, simulating a stretch-shortening cycle. The length ratio between the CE and the SEE, the size of the mass and the initial length of the CE were sequentially changed. As a result, it was found that a higher performance is obtained with a longer SEE when the mass is small, while with a shorter SEE when the mass is large.