Abstract: Analyzed in the essay are the service behaviors and failure type of the casing as used for the cyclic steam stimulation thermal well of a certain domestic oil field. Accordingly，a strain-based design idea for the casing string is proposed. The method for the design mainly focuses on the longitudinal deformation of the casing string，and is used to allow the material to develop plastic deformation within the specific safety margin. Furthermore， the reasonability of the said design for the casing string is verified via actual service cases.