Hot deformation behavior of powder metallurgical high tungsten alloy steel was investigated by Gleeble thermal simulator in a temperature range of 900~1100 °C and a strain rate range of 0.001~1 s^-1. The results show that the flow stress decreases with the decrease of strain rate and the increase of deformation temperature. A constitutive equation is derived with Arrhenius hyperbolic sine function, and a processing map is constructed. The activation energy is 377 kJ/mol. The suitable processing regions are 1000~1100 °C/0.001~0.01 s^-1. The precipitation of tungsten-rich μ phase occurs during hot deformation process. Microvoids and micro-cracks form in the bulging region of the specimen. The amount of microvoid increases with the increase of strain rate and the decrease of temperature. The μ phase precipitation improves the high temperature strength of the steel.