The influence of solidification pressure on the thermodynamic and kinetic parameters of 19Cr14Mn4Mo0.9N high nitrogen steel is clarified by Thermo‐Calc/DICTRA software, including phase diagram, solidification mode, liquidus/solidus temperature, nitrogen solubility, partition coefficient, diffusion coefficient, driving force for nucleation, and diffusion coefficient. On this basis, the effect of pressure on critical nucleation radius and nucleation rate is also revealed. In the calculated vertical sections of 19Cr14Mn4Mo‐xN alloy phase diagram, δ single‐phase region decreases, both γ single‐phase region and three‐phase region L + δ + γ increase with increasing pressure. Additionally, the reaction mode of solidification transition gradually turns from peritectic to eutectic reaction, and the solidification mode changes from FA to A mode. Increasing the partial pressure of nitrogen can suppress the formation of ferrite trap and increase nitrogen solubility. Meanwhile, the partition coefficients of C, N, Cr, and Si increase, that of Mn and Mo decreases, resulting in decrease of C, N, and Cr microsegregation and improvement of Si, Mn, and Mo microsegregation. Pressurization has a small impact on diffusion coefficients, but it obviously promote the driving force for produced phase (δ and γ) nucleation, this lead to the decrease of critical nucleation radius, improvement of nucleation rate, and grain refinement of 19Cr14Mn4Mo0.9N high nitrogen steel.