Abstract: The large LOCA blowdown simulation experiment is usually needed for the purpose of the performance evaluation of containment sump strainer and downstream effect analysis. In this paper, large LOCA blowdown simulation experiment was conducted by double rupture discs combining with a pneumatic valve, and the accurate controlling of starting pressure and the instantaneous release of high-energy fluid was realized. The measurement results of dynamic pressure indicate that the pressure lose of double discs bleed starting mode is the largest, and the total pressure rise velocity is relative slow for the single disc starting mode. Double discs charging starting mode can accurately simulate large LOCA blowdown physical process in term of pressure loss, pressure rise velocity and pressure accuracy. Finally, jet impinging destruction tests for double-wall encapsulated insulation configuration were carried out by double discs charging starting mode. The results indicate that the impact load supplied by the present facility is sufficient.