Abstract: The high temperature deformation behavior of SAE8620 H gear steel in a temperature range of 950 to 1100℃ and a strain rate range of 0.01 to 10 s^-1 was studied by high temperature compression tests. The flow stress of the steel has steady state characteristics. The flow stress decreases with the increase of deformation temperature and the decrease of strain rate. The constitutive equation of the steel can be described by a hyperbolic sine equation. Based on the related data of peak stress,strain rate and temperature,the hot deformation activation energy of the steel was deduced to be about 280359.9 J·mol^-1. The processing maps were drawn according to 40% and 60% deformation. The forming parameters can be determined by the processing maps. Low strain rate should be used for small deformation,while high strain rate and high forming temperature or low strain rate and low forming temperature should be used for large deformation.