Abstract: Liquid-sealer experiment facility was designed and built in order to test the safety of the main vessel liquid-sealer on China Experimental Fast Reactor (CEFR). Overpressure protection action experiment, negative pressure action experiment, residual pressure experiment after overpressure action and gas exhausting capability experiment of main vessel liquid sealer were carried out on the experiment facility. Through the experiments, lots of important parameters of the pressure and gas flow were obtained. The analysis of the experiment performance and results provides credible basis of the practical use of the liquid sealer on CEFR.