Abstract: Conducted are relevant comparative analysis relating load of pipe bodied of casing and drill pipe,their failure types and the required Charpy impact energy values.Discussed are the differences between the Charpy impact energy value of the extra-hi-strength casing and those of the drill pipe and the drill stem elements,on the basis of the analysis.Particularly discussed is the suitability of the imperial equation indicating that the average Charpy impact energy value is 1/10 of the lower limit value of yield strength.The co-authors regard that it is hamful,and practically and theoretically groundless to further apply the said imperial equation to the deep wellservice extra-hi-strength casing and casing string which have quite different load status and failure type.Any unsuitable and excessively critical requirement for toughness of the deep well-service extra-hi-strength casing can do nothing but lead to function surplus and increase of manufacture cost.