Thispaperexaminestheimpactofforeignpenetrationonthepublicfirminamixedoligopolisticmarket.Throughtheestablishmentofamixeddoubleoligopolymarket,thispaperanalyzeshowtheshareofforeigninvestmentaffectstheenvironmentalpolicy,thepollutantemission,andthesocialwelfareundertheconditionofthestatetax.Theresultsshowthat:first,theintroductionofforeigninvestmenthassomecrowding-outeffectsonthesociallevelofoutput.Second,theentryofforeigninvestmentincreasestheprofitofthepublicfirmbyalargemargin,andthemaximumprofitoftheprivatefirmhasbeenreduced.Third,theincreaseofforeigninvestmentinpublicfirmdoesnotnecessarilyimprovetheenvironment.
