The nickel-free high nitrogen austenitic Cr18Mn16Mo2.5N0.83Nb0.15 stainless steel was fabricated by electroslag remelting technology. The high-temperature thermal deformation behavior of as-fabricated steel was investigated using Gleeble-1500D type thermal-mechanical simulation testing machine under the condition of the temperature range from 950℃ to 1100℃ and the strain-rate range from 0.01s-1 to 1.0s-1. The constitutive equation containing polynomial of as-fabricated steel was built to describe stress function containing the variable of deformation temperature and strain-rate based on Arrhenius equation. The Q value is 448.915 kJ/mol by computing using the experimental data obtained from the thermal deformation tests. The thermal forging temperature should be higher than 1050 ℃ and the strain-rate below 1s-1 based on the thermal processing maps.