Hydrogen solubility of FLiNaK (LiF 46.5 mol% + NaF 11.5% + KF 42 mol%) were investigated with hydrogen plasma interaction. To use molten salt as liquid wall for fusion device, tritium retention property of the molten salt should be studied. Although there have been some reports on hydrogen solubility of FLiNaK, retention property of FLiNaK with hydrogen plasma interaction has not been reported yet. Hydrogen outgassing of molten FLiNaK was measured with RGA after interaction of hydrogen plasma. Hydrogen partial pressure of the RGA was calibrated with an H2 mass flow controller of 5sccm. Hydrogen plasma was generated with 500W ECR source and the molten FLiNaK was contained with heated crucible of diameter of 46mm and depth of 40mm. By measuring hydrogen ion density near the surface of FLiNaK, we evaluated dose of hydrogen to the FLiNaK and calculated retention percentage with measured outgassing amount of hydrogen. Compared to Henry's law, plasma-interacted-FLiNaK showed significantly large amount of hydrogen retention such as 10000 times.