Hot deformation behavior of GH738 superalloy was studied in the temperature range of 1000~1160 oC, strain rate range of 0.01 ~10 s-1 and engineering strain range 15%~70% by the Gleeble-1500 simulator. The hot deformation equation was determined to characterize the dependence of peak stress on the temperature and strain rate. Processing maps for hot working were established on the basis of the variations of efficiency of power dissipation with temperature and strain rate, and interpreted according to the microstructure observation. The apparent activation energy Q of GH738 superalloy is about 499 kJ/mol. The maps obtained in true strain range from 0.2 to 0.8 are essentially different, and the efficiency of power dissipation increases gradually with the increase of temperature and the decrease of strain rate. An optimum zone named safe area is obtained for GH738 alloy deformation. The above results can be used as a reference for hot working of GH738 superalloy.