In this study, the electrical properties of as-deposited Sr0.4Ba0.6Nb2O6 (SBN) ferroelectric thin films on SiO2/Si(100) substrates were improved by low temperature supercritical carbon dioxide fluid (SCF) process treatment. The as-deposited SBN ferroelectric thin films were treated by SCF process which mixed with pure H2O and propyl alcohol. After SCF process treatment, the memory windows increased in C-V curves, and the passivation of oxygen vacancy and defect in leakage current density curves were obtained. In addition, the improvement properties of as-deposited SBN thin films after SCF process treatment were found by XPS, C-V, and J-E measurement. Finally, the mechanism concerning the dependence of electrical properties of the SBN ferroelectric thin films on the SCF process was discussed.