In the context of integrated die-casting forming technology for new energy vehicles， a new type of extra-large， highly uniform， high-toughness， and high- isotropy die-casting mold steel GY-DCK20 was developed and produced. The microstructural uniformity of samples taken from different locations and their room-temperature mechanical properties were investigated by characterization methods such as metallographic analysis， SEM analysis， and ASPEX inclusion analysis. The results indicate that the high-cleanliness smelting process （EAF +AOD） → RH → Continuous Casting → PESR effectively controls the content of harmful and gaseous elements. Fine inclusions measuring 2-5 μm account for over 73.4% of the total， with oxides being the primary type. No significant banding segregation was observed in samples taken from different locations； the spheroidized microstructure was well-developed， and carbides were fine and uniformly distributed. The heat-treated hardness after quenching at 1 030 ℃ was approximately 1HRC higher than that at 1 010 ℃， and the steel exhibited better impact performance. During the tempering stage， the secondary hardening peak occurred near 540 °C， primarily due to the precipitation of fine， granular alloy carbides； at 650 ℃， martensite began to undergo recovery and recrystallization， forming equiaxed ferrite grains； at 700 ℃， the lath structure of the martensite disappeared， carbides aggregated along the grain boundaries， and recrystallized grains coarsened significantly. At a service hardness of 44-46HRC， the test steel exhibits a transverse and longitudinal V-notch impact absorbed energy of over 35 J at various locations， with an isotropy ratio of up to 0.97 in the core， demonstrating excellent comprehensive mechanical properties.