A method of manufacturing an automobile part, comprising: preparing blank sheets using steel sheets subjected to heat-treatment hardening and having different thicknesses or different material properties according to desired strength; forming a blank assembly by joining the blank sheets to each other via laser welding; cold-pressing the blank assembly; and heating the cold-pressed part to a temperature of AC 3 or more, followed by quenching the cold-pressed part received within dies to remove residual stress while increasing strength of the automobile part, wherein the steel sheets in preparation of the blank sheets comprise at least one composition consisting of a first composition, a second composition, a third composition, a fourth composition and a fifth composition, wherein the first composition is 0.15 to 0.5 wt% of carbon, 0.15 to 0.5 wt% of silicon (Si), 0.5 to 3.0 wt% of manganese (Mn), 0.1 wt% or less of phosphorous, 0.1 wt% or less of sulfur, 0.01 to 1.0 wt% of chromium (Cr), 0.2 wt% or less of titanium (Ti), 0.1 wt% or less of aluminum (Al), 0.0005 to 0.08 wt% of boron, and the balance of Fe and unavoidable impurities, wherein the second composition is 0.15 to 0.4 wt% of carbon, 0.03 to 0.4 wt% of silicon (Si), 1.0 to 2.0 wt% of manganese (Mn), 0.12 wt% or less of phosphorous, 0.003 wt% or less of sulfur, 0.0005 to 0.08 wt% of boron, 0.005 to 0.1 wt% of zirconium (Zr), 0.001 to 0.005 wt% of calcium (Ca), and the balance of Fe and unavoidable impurities, wherein the third composition is 0.15 to 0.30 wt% of carbon, 0.05 to 0.5 wt% of silicon (Si), 1.0 to 2.0 wt% of manganese (Mn), 0.0005 to 0.0040 wt% of boron, 0.003 wt% or less of sulfur, 0.012 wt% or less of phosphorous, at least two components selected from among cobalt (Co), zirconium (Zr) and antimony (Sb), and the balance of Fe and unavoidable impurities, wherein the fourth composition is 0.15 to 0.40 wt% of carbon, 0.03 to 0.30 wt% of silicon (Si), 1.0 to 2.0 wt% of manganese (Mn), 0.0005 to 0.004 wt% of boron, optionally, at least one of 0.003 wt% or less of sulfur, 0.012 wt% or less of phosphorous, 0.001 to 0.005 wt% of calcium (Ca), 0.005 to 0.05 wt% of niobium (Nb), 0.005 to 0.1 wt% of zirconium (Zr) and 0.0005 to 0.5 wt% of cobalt (Co), and the balance of Fe and unavoidable impurities, wherein the fifth composition is 0.19 to 0.40 wt% of carbon, 0.5 to 2.5 wt% of manganese (Mn), 0.1 to 0.5 wt% of chromium (Cr), 0.0015 to 0.0040 wt% of boron, 0.01 to 0.5 wt% of silicon (Si), 0.05 wt% or less of phosphorous, 0.05 wt% or less of sulfur, 0.03 wt% or less of aluminum (Al), one or two components selected from among 0.01 to 2 wt% of nickel (Ni), 0.01 to 0.10 wt% of niobium (Nb), 0.01 to 1 wt% of copper (Cu) and 0.01 to 0.20 wt% of molybdenum (Mo), and the balance of Fe and unavoidable impurities. preparing blank sheets using steel sheets subjected to heat-treatment hardening and having different thicknesses or different material properties according to desired strength; forming a blank assembly by joining the blank sheets to each other via laser welding; cold-pressing the blank assembly; and heating the cold-pressed part to a temperature of AC 3 or more, followed by quenching the cold-pressed part received within dies to remove residual stress while increasing strength of the automobile part, wherein the steel sheets in preparation of the blank sheets comprise at least one composition consisting of a first composition, a second composition, a third composition, a fourth composition and a fifth composition, wherein the first composition is 0.15 to 0.5 wt% of carbon, 0.15 to 0.5 wt% of silicon (Si), 0.5 to 3.0 wt% of manganese (Mn), 0.1 wt% or less of phosphorous, 0.1 wt% or less of sulfur, 0.01 to 1.0 wt% of chromium (Cr), 0.2 wt% or less of titanium (Ti), 0.1 wt% or less of aluminum (Al), 0.0005 to 0.08 wt% of boron, and the balance of Fe and unavoidable impurities, wherein the second composition is 0.15 to 0.4 wt% of carbon, 0.03 to 0.4 wt% of silicon (Si), 1.0 to 2.0 wt% of manganese (Mn), 0.12 wt% or less of phosphorous, 0.003 wt% or less of sulfur, 0.0005 to 0.08 wt% of boron, 0.005 to 0.1 wt% of zirconium (Zr), 0.001 to 0.005 wt% of calcium (Ca), and the balance of Fe and unavoidable impurities, wherein the third composition is 0.15 to 0.30 wt% of carbon, 0.05 to 0.5 wt% of silicon (Si), 1.0 to 2.0 wt% of manganese (Mn), 0.0005 to 0.0040 wt% of boron, 0.003 wt% or less of sulfur, 0.012 wt% or less of phosphorous, at least two components selected from among cobalt (Co), zirconium (Zr) and antimony (Sb), and the balance of Fe and unavoidable impurities, wherein the fourth composition is 0.15 to 0.40 wt% of carbon, 0.03 to 0.30 wt% of silicon (Si), 1.0 to 2.0 wt% of manganese (Mn), 0.0005 to 0.004 wt% of boron, optionally, at least one of 0.003 wt% or less of sulfur, 0.012 wt% or less of phosphorous, 0.001 to 0.005 wt% of calcium (Ca), 0.005 to 0.05 wt% of niobium (Nb), 0.005 to 0.1 wt% of zirconium (Zr) and 0.0005 to 0.5 wt% of cobalt (Co), and the balance of Fe and unavoidable impurities, wherein the fifth composition is 0.19 to 0.40 wt% of carbon, 0.5 to 2.5 wt% of manganese (Mn), 0.1 to 0.5 wt% of chromium (Cr), 0.0015 to 0.0040 wt% of boron, 0.01 to 0.5 wt% of silicon (Si), 0.05 wt% or less of phosphorous, 0.05 wt% or less of sulfur, 0.03 wt% or less of aluminum (Al), one or two components selected from among 0.01 to 2 wt% of nickel (Ni), 0.01 to 0.10 wt% of niobium (Nb), 0.01 to 1 wt% of copper (Cu) and 0.01 to 0.20 wt% of molybdenum (Mo), and the balance of Fe and unavoidable impurities.