Vacuum system of J-PARC Rapid Cycling Synchrotron (RCS) has been operating since 2007. There had been almost no trouble since then, so the actual system behaviour in case of unexpected trouble has not been examined. However, the J-PARC site was hit by the Great East Japan Earthquake in March 2011. Though accident analysis and recovery work, we investigated whether the system behaved correctly and how much damage the devices are sustained. We also summarize the results of the investigation about the dynamic pressure, which is caused by the high power beam and other elements.