Supply of tritium for initial loading was concerned to be a limit for fusion power plant to increase its number in the future. In order to consider the implication of the possible tritium self-production, the potential of fusion energy in the future electricity supply market was estimated. Future energy market is analyzed with world energy and environment model that describes composition of supply-side energy system structures under economical and environmental constraint to meet the world energy demand. In the model, composition of supply-side energy system structures is determined to limit the CO2 concentration of 550ppm in 2100 with minimal energy system cost. The result revealed that after introduction to the market, share of the fusion energy is strongly restricted by the initial tritium supply. Capability to produce initial loading of tritium removes this limitation, and future fusion share could be doubled.