Abstract: Plasma arc cutting technology is widely used in industrial fields because of its efficient and stable process advantages. Taking the air plasma arc as the research object, this paper establishes a two-dimensional axisymmetric finite element mathematical model of the nozzle structure through COMSOL multiphysics software, and optimizes the arc magnetic fluid model. Based on magnetohydrodynamics and arc plasma theory, the multi physical field interface of plasma equilibrium discharge is selected, and the control equations and boundary conditions of air plasma arc model are established to realize the compilation and solution of the arc model. The simulation results show that under the condition of consistent arc starting current, the arc shrinks in temperature distribution and velocity distribution with the increase of ambient pressure. Based on the 3 MPa high-pressure welding test chamber, an experimental system of plasma arc cutting in high-pressure environment is built. Through the optimization design of gas circuit and non high-frequency arc starting circuit, the stable arc starting with environmental pressure of 0.1 ~ 0.7 MPa is realized. Based on this, plasma arc cutting experiments under high pressure gradient were carried out, and the influence of environmental pressure on plasma arc ionization behavior was studied combined with cutting quality index.