The initial tritium supply for starting up FDS-II was done by using the Tritium Analysis Software (TAS) developed by FDS Team. The results showed that the initial tritium supply for startup was strongly dependent on the tritium burn-up fraction in plasma and mean residence time of tritium in the plasma exhaust processing system. Considering the sensitive analysis and other advanced designs, the tritium burn-up fraction in plasma was selected to be 0.1 for FDS-II. The minimum initial tritium supply for startup was ~4.2kg. Considering the potential malfunction in the fuel cycle system and assuming the reactor ran continuously before solving the malfunction, it was reasonable to keep the initial tritium supply for FDS-II as ~8.9kg.