Based　on　the　1-D　&　2-D　combined　computational　model,　numerical　optimizing　analyses　on　the　performance　of　the　orifice　type　pulse　tube　refrigerator　(OPTR)　and　double-inlet　type　pulse　tube　refrigerator　(DPTR)　were　carried　out.　The　evolvements　process　of　the　flow　field　in　the　OPTR　and　DPTR　were　examined.　The　results　show　that　in　the　compressor　expansion　process　the　gas　separation　phenomenon　occurs　in　the　pulse　tube,　and　in　the　compression　process,　there　exists　the　gas　aggregation　phenomenon.　The　gas　velocities　in　the　separation　and　aggregation　interfaces　are　zero,　so　the　interface　is　called　zero　interface.　In　a　period,　the　zero　interface　will　move　from　one　end　of　the　pulse　tube　to　the　other　end,　which　is　called　zero　interface　effect.　The　zero　interface　effect　is　an　important　factor　for　the　performance　enhancement　of　the　PTR.　The　longer　the　time　of　the　zero　interface　effect　existing　in　a　period,　the　better　the　PTR　performance.　Then　based　on　the　simulation　results,　the　mechanism　analysis　for　the　existing　of　zero　interface　effect　was　performed.　The　results　show　that　the　introduction　of　the　orifice　valve　leads　to　the　formation　of　zero　interface　effect　and　the　introduction　of　the　double-inlet　valve　could　augment　the　zero　interface　effect.　For　the　OPTR,　the　time　of　the　zero　interface　existing　is　about　1/6　period　and　for　the　DPTR　the　existing　time　of　the　zero　interface　is　about　1/2　period.