Abstract: The influences of the austempering time and tempering temperature on the strength and toughness of S135 drill pipe material when it is heat treated with the austempering and tempering process are studied. The result shows that,with the raise of tempering temperature and the prolongation of austempering time,its tensile strength and yield strength are decreased while its ductility and toughness are increased. However,the austempering time and low or medium temperature tempering do not have an obvious effect on its toughness. The heat treatment process which obviously improves the toughness of drill pipe material is described. Compared with its original properties,the yield strength of S135 drill pipe material is the same as before or 3.5% lower than before but its toughness is obviously increased up to 38% after it is processed with this heat treatment technology.