A separator for electrochemical device, characterized in that the separator comprises: an irradiation crosslinked fluoropolymer A with a melting point above 150°C and/or a polymer B containing a benzene ring in its main chain; an ultrahigh molecular weight polyethylene having a molecular weight of 1.0×10 6 - 10.0×10 6 ; a high density polyethylene having a density in the range of 0.940-0.976 g/cm 3 ; and crosslinking agent; the fluoropolymer A with a melting point above 150°C is selected from the group consisting of polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, propylene-tetrafluoroethylene copolymer, fluorinated ethylene-propylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene terpolymer; the polymer B having a benzene ring in its main chain is selected from the group consisting of: poly(paraphenylene terephthalamide), polyaryl ether sulfone, polyaryl sulfone, polyether sulfone, polyarylene sulfide sulfone, polyether ether ketone, polyether ketone, polyether ketone ketone, polyether ether ketone ketone, polyether ketone ether ketone ketone, polyphenylene ether, polyphenylene sulfide, polyaryl ester, polyphenyl ester, semi-aromatic or aromatic polyimides, semi-aromatic or aromatic polyamides, polyetherimides, and polyamideimides; the crosslinking agent is one or more selected from the group consisting of mercaptobenzothiazole, benzothiazolyl disulfide, N-cyclohexylbenzothiazole sulfenamide, oxydivinylbenzothiazole sulfenamide, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, diphenylguanidine, di-o-tolylguanidine, ethylenethiourea, N,N'-diethyl thiourea, hexamethylenetetramine, zinc isopropyl xanthate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyl cyanurate, and triallyl isocyanurate; and the separator for electrochemical device has a temperature difference between pore closing temperature and film breaking temperature of 80-90°C, and a heat shrinkage of 2.0% or less. the fluoropolymer A with a melting point above 150°C is selected from the group consisting of polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, propylene-tetrafluoroethylene copolymer, fluorinated ethylene-propylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene terpolymer; the polymer B having a benzene ring in its main chain is selected from the group consisting of: poly(paraphenylene terephthalamide), polyaryl ether sulfone, polyaryl sulfone, polyether sulfone, polyarylene sulfide sulfone, polyether ether ketone, polyether ketone, polyether ketone ketone, polyether ether ketone ketone, polyether ketone ether ketone ketone, polyphenylene ether, polyphenylene sulfide, polyaryl ester, polyphenyl ester, semi-aromatic or aromatic polyimides, semi-aromatic or aromatic polyamides, polyetherimides, and polyamideimides; the crosslinking agent is one or more selected from the group consisting of mercaptobenzothiazole, benzothiazolyl disulfide, N-cyclohexylbenzothiazole sulfenamide, oxydivinylbenzothiazole sulfenamide, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, diphenylguanidine, di-o-tolylguanidine, ethylenethiourea, N,N'-diethyl thiourea, hexamethylenetetramine, zinc isopropyl xanthate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyl cyanurate, and triallyl isocyanurate; and the separator for electrochemical device has a temperature difference between pore closing temperature and film breaking temperature of 80-90°C, and a heat shrinkage of 2.0% or less. <EOS>