Abstract: Sodium filling into fuel test capsules is essential in the fuel research for fast reactor. According to the filling requirement and the properties of sodium, a sodium filling device and an inert-gas glove box which adopted vacuum, temperature-controlling and inert gas protection were designed. PTFE ring which could avoid the damage of hard connection was tested to solve the seal problem between sodium filling device and fuel test capsules at high temperature. The filling amount MAD and MRSD of seven simulate experiments were 0.03 g and 0.08%, respectively, which meet the demand of sodium filling into fuel test capsules. The results of industrial CT scanning, dissection and remained sodium comparison show that the sodium filling is satisfied. A single sodium filling process costs 2 h averagely, so it is practical for meeting the small batch sodium filling demands. This sodium filling device can be applied to other liquid metal filling into a thin pipeline as well.