A method for forming a multilayer coating film comprising: applying one or more base coating compositions in at least one layer to a substrate to form a base coating film in at least one layer; applying one or more clear coating compositions to the above uncured base coating film formed in at least one layer; and simultaneously curing the at least one layer of uncured base coating film and the above uncured clear coating film, wherein the one or more clear coating compositions comprises: a hydroxy-containing acrylic resin having a hydroxy value in the range of 85 to 215 mg KOH/g, a polyisocyanate compound having a viscosity at 25°C in the range of 200 to 4,000 mPa·s and having at least two isocyanate groups per molecule, and an organometallic catalyst containing a metallic compound in which the metal is a member selected from the group consisting of zinc, tin, zirconium, bismuth, lead, cobalt, manganese, titanium, aluminum and molybdenum, and an amidine compound, wherein the equivalent ratio (NCO/OH) of isocyanate groups in the polyisocyanate compound to hydroxy groups in the hydroxy-containing acrylic resin is in the range of 0.8 to 1.8 and the amidine compound comprises at least one member selected from the group consisting of 1,5-diazabicyclo(4.3.0)non-5-ene, 1,8-diazabicyclo(5.4.0)undec-7-ene, 1,4-diazabicyclo(3.3.0)oct-4-ene, 2-methyl-1,5-diazabicyclo(4.3.0)non-5-ene, 2,7,8-trimethyl-1,5-diazabicyclo(4.3.0)non-5-ene, 2-butyl-1,5-diazabicyclo(4.3.0)non-5-ene, 1,9-diazabicyclo(6.5.0)tridec-8-ene and an imidazole derivative represented by the following structural formula: wherein R 5, R 6, R 7, and R 8 are each independently hydrogen, alkyl, substituted alkyl, hydroxyalkyl, allyl, aralkyl, cycloalkyl, a heterocyclic ring, ether, thioether, halogen, -N 2, polyethylene polyamine, nitro, keto, ester, carbonamide, or these functional groups substituted with alkyl. applying one or more base coating compositions in at least one layer to a substrate to form a base coating film in at least one layer; applying one or more clear coating compositions to the above uncured base coating film formed in at least one layer; and simultaneously curing the at least one layer of uncured base coating film and the above uncured clear coating film, wherein the one or more clear coating compositions comprises: a hydroxy-containing acrylic resin having a hydroxy value in the range of 85 to 215 mg KOH/g, a polyisocyanate compound having a viscosity at 25°C in the range of 200 to 4,000 mPa·s and having at least two isocyanate groups per molecule, and an organometallic catalyst containing a metallic compound in which the metal is a member selected from the group consisting of zinc, tin, zirconium, bismuth, lead, cobalt, manganese, titanium, aluminum and molybdenum, and an amidine compound, wherein the equivalent ratio (NCO/OH) of isocyanate groups in the polyisocyanate compound to hydroxy groups in the hydroxy-containing acrylic resin is in the range of 0.8 to 1.8 and the amidine compound comprises at least one member selected from the group consisting of 1,5-diazabicyclo(4.3.0)non-5-ene, 1,8-diazabicyclo(5.4.0)undec-7-ene, 1,4-diazabicyclo(3.3.0)oct-4-ene, 2-methyl-1,5-diazabicyclo(4.3.0)non-5-ene, 2,7,8-trimethyl-1,5-diazabicyclo(4.3.0)non-5-ene, 2-butyl-1,5-diazabicyclo(4.3.0)non-5-ene, 1,9-diazabicyclo(6.5.0)tridec-8-ene and an imidazole derivative represented by the following structural formula: wherein R 5, R 6, R 7, and R 8 are each independently hydrogen, alkyl, substituted alkyl, hydroxyalkyl, allyl, aralkyl, cycloalkyl, a heterocyclic ring, ether, thioether, halogen, -N 2, polyethylene polyamine, nitro, keto, ester, carbonamide, or these functional groups substituted with alkyl. a hydroxy-containing acrylic resin having a hydroxy value in the range of 85 to 215 mg KOH/g, a polyisocyanate compound having a viscosity at 25°C in the range of 200 to 4,000 mPa·s and having at least two isocyanate groups per molecule, and an organometallic catalyst containing a metallic compound in which the metal is a member selected from the group consisting of zinc, tin, zirconium, bismuth, lead, cobalt, manganese, titanium, aluminum and molybdenum, and an amidine compound, wherein the equivalent ratio (NCO/OH) of isocyanate groups in the polyisocyanate compound to hydroxy groups in the hydroxy-containing acrylic resin is in the range of 0.8 to 1.8 and the amidine compound comprises at least one member selected from the group consisting of 1,5-diazabicyclo(4.3.0)non-5-ene, 1,8-diazabicyclo(5.4.0)undec-7-ene, 1,4-diazabicyclo(3.3.0)oct-4-ene, 2-methyl-1,5-diazabicyclo(4.3.0)non-5-ene, 2,7,8-trimethyl-1,5-diazabicyclo(4.3.0)non-5-ene, 2-butyl-1,5-diazabicyclo(4.3.0)non-5-ene, 1,9-diazabicyclo(6.5.0)tridec-8-ene and an imidazole derivative represented by the following structural formula: wherein R 5, R 6, R 7, and R 8 are each independently hydrogen, alkyl, substituted alkyl, hydroxyalkyl, allyl, aralkyl, cycloalkyl, a heterocyclic ring, ether, thioether, halogen, -N 2, polyethylene polyamine, nitro, keto, ester, carbonamide, or these functional groups substituted with alkyl.