A method of preparing a polyolefin resin, the method comprising: a) synthesizing a pre-polymer in a slurry polymerization reactor by pre-polymerization of a pre-polymerization composition comprising an ethylene monomer, an alpha olefin monomer having 3 or more carbon atoms, and a catalyst composition; and b) synthesizing a polyolefin polymer by polymerizing supplied a main polymerization composition comprising the pre-polymer, an ethylene monomer, and a 1-hexene comonomer to a gas phase reactor, wherein the polyolefin polymer satisfies the following requirements (i) to (vii): (i) a density D measured by a density gradient pipe method according to ASTM D1505 ranges from 0.915 to 0.933 g/cm 3; (ii) a melt flow index MIE measured according to ASTM D1238 at 190°C and a load of 2.16 kg ranges from 0.3 to 1.0 g/10 minutes; (iii) a high load melt flow index MIF measured according to ASTM D1238 at 190°C and a load of 21.6 kg ranges from 17 to 35 g/10 minutes; (iv) a melt flow rate ratio SR, according to SR = MIF/MIE, ranges from 40 to 50; (v) a ratio Mw/Mn of a weight average molecular weight Mw to a number average molecular weight Mn measured by gel permeation chromatography ranges from 3.0 to 5.0; (vi) a ratio Mz/Mw of a Z-average molecular weight Mz to a weight average molecular weight Mw measured by gel permeation chromatography ranges from 2.0 to 3.5; and (vii) a tear strength MD measured by ASTM D-1922 in a machine direction of a film produced by blowing the polyolefin resin to a thickness of 30 um at an expansion ratio BUR of 2.5 satisfies Relational Expression 1 below. MD > 1 EXP 0.102 × SR × 3000 + EXP 4.35 D, characterized in that the catalyst composition comprises one or more organometallic compound represented by Chemical Formula 1 below: in Chemical Formula 1, M is zirconium, L 1 and L 2 are each independently cyclopentadienyl, indenyl, tetrahydroindenyl or fluorenyl, T is Al, Si, Sn, or a hydrocarbon group having 1 to 4 carbon atoms, X 1 and X 2 are each independently a halogen or a hydrocarbon group having 1 to 10 carbon atoms, and L 1, L 2, and T are each independently unsubstituted or further substituted with hydrogen, halogen, hydrocarbyl having 1 to 20 carbon atoms, alkoxy having 1 to 20 carbon atoms, or any combination thereof, in which substituents adjacent to each other are each independently linked to L 1 and L 2, thereby forming a fused ring structure, and the catalyst composition comprises one or more aluminoxanes represented by Chemical Formulas 2 to 4 below: in Chemical Formulas 2, 3, and 4, R 1 to R 4 each independently are a linear or branched alkyl group having 1 to 10 carbon atoms, X and y each independently are integers in the range of 1 to 50, and z is an integer in the range of 3 to 50. a) synthesizing a pre-polymer in a slurry polymerization reactor by pre-polymerization of a pre-polymerization composition comprising an ethylene monomer, an alpha olefin monomer having 3 or more carbon atoms, and a catalyst composition; and b) synthesizing a polyolefin polymer by polymerizing supplied a main polymerization composition comprising the pre-polymer, an ethylene monomer, and a 1-hexene comonomer to a gas phase reactor, (i) a density D measured by a density gradient pipe method according to ASTM D1505 ranges from 0.915 to 0.933 g/cm 3; (ii) a melt flow index MIE measured according to ASTM D1238 at 190°C and a load of 2.16 kg ranges from 0.3 to 1.0 g/10 minutes; (iii) a high load melt flow index MIF measured according to ASTM D1238 at 190°C and a load of 21.6 kg ranges from 17 to 35 g/10 minutes; (iv) a melt flow rate ratio SR, according to SR = MIF/MIE, ranges from 40 to 50; (v) a ratio Mw/Mn of a weight average molecular weight Mw to a number average molecular weight Mn measured by gel permeation chromatography ranges from 3.0 to 5.0; (vi) a ratio Mz/Mw of a Z-average molecular weight Mz to a weight average molecular weight Mw measured by gel permeation chromatography ranges from 2.0 to 3.5; and (vii) a tear strength MD measured by ASTM D-1922 in a machine direction of a film produced by blowing the polyolefin resin to a thickness of 30 um at an expansion ratio BUR of 2.5 satisfies Relational Expression 1 below. M is zirconium, L 1 and L 2 are each independently cyclopentadienyl, indenyl, tetrahydroindenyl or fluorenyl, T is Al, Si, Sn, or a hydrocarbon group having 1 to 4 carbon atoms, X 1 and X 2 are each independently a halogen or a hydrocarbon group having 1 to 10 carbon atoms, and L 1, L 2, and T are each independently unsubstituted or further substituted with hydrogen, halogen, hydrocarbyl having 1 to 20 carbon atoms, alkoxy having 1 to 20 carbon atoms, or any combination thereof, in which substituents adjacent to each other are each independently linked to L 1 and L 2, thereby forming a fused ring structure, and the catalyst composition comprises one or more aluminoxanes represented by Chemical Formulas 2 to 4 below: in Chemical Formulas 2, 3, and 4, R 1 to R 4 each independently are a linear or branched alkyl group having 1 to 10 carbon atoms, X and y each independently are integers in the range of 1 to 50, and z is an integer in the range of 3 to 50. R 1 to R 4 each independently are a linear or branched alkyl group having 1 to 10 carbon atoms, X and y each independently are integers in the range of 1 to 50, and z is an integer in the range of 3 to 50.