In D-3He fusion, most of fusion energy is carried by created protons of 14.7MeV. Concept of traveling wave direct energy converter (TWDEC) is applied for the purpose to construct an energy converter with less handling voltage and higher efficiency. To improve conversion efficiency of the TWDEC, we propose two methods of optimization of decelerator structure in the view point of matching between the beam velocity and the phase velocity of the traveling wave. As the result of experiments in a TWDEC simulator based on each method, these optimizations are really effective to improve conversion efficiency. However, when the matching is disturbed by some factors, less matching results in less efficiency.