In this paper, a novel method of pressurized metallurgy technology was proposed to improve cast structure of M42 high speed steel (HSS). The effect of solidification pressure (0.1, 1 and 2 MPa) on the cast structure of M42 HSS was investigated by means of experimental analysis and calculation of Thermo-Calc and DICTRA software. Increasing solidification pressure can obviously enhance cooling rate by improving interfacial heat transfer coefficient, which results in some remarkable improvement of the cast structure of M42 HSS. Firstly, the primary/secondary dendrite arm spacing and the average thickness of eutectic ledeburite reduce, which means dendrite structure is refined and eutectic ledeburite more homogeneously distributes with smaller size. Secondly, increasing solidification pressure, the volume fraction of M₆C carbides decreases obviously and that of M₂C increases correspondingly. And the morphology of M₂C carbide changes from larger size lamellar and straight-rod shape into smaller size curved-rod morphology under higher solidification pressure due to larger nucleation number and overgrowth of γ, indicating that carbides are refined and distribute more uniformly. At last, higher solidification pressure is beneficial to reduce the lamellar spacing of M₂C carbide and make compositions distribute more homogeneously.