The　main　contribution　of　this　work　is　to　propose　a　primal-dual　combinatorial　3(1　+　epsilon)-approximation　algorithm　for　the　two-level　facility　location　problem　(2-LFLP)　by　exploring　the　approximation　oracle　concept.　This　result　improves　the　previous　primal-dual　6-approximation　algorithm　for　the　multilevel　facility　location　problem,　and　also　matches　the　previous　primal-dual　approximation　ratio　for　the　single-level　facility　location　problem.　One　of　the　major　merits　of　primal-dual　type　algorithms　is　their　easy　adaption　to　other　variants　of　the　facility　location　problems.　As　a　demonstration,　our　primal-dual　approximation　algorithm　can　be　easily　adapted　to　several　variants　of　the　2-LFLP,　including　models　with　stochastic　scenario,　dynamically　arrived　demands,　and　linear　facility　cost.　(C)　2014　Elsevier　B.V.　All　rights　reserved.