Abstract: Described here in the essay are the calculation criteria and the common-used formula for the connection strength of the oil tubing and casing.Also analyzed and discussed are the critical parameters concerning the said connection strength computation,including coupling dangerous cross section,pipe body dangerous cross section,yield strength and tensile strength. It is regarded via the analysis that the structural parameters(i.e.,coupling dangerous cross section and pipe body dangerous cross section)are related to the data like the thread connection,the thread profile and the make up position,etc. It is conclusively regarded that the material parameters (i.e.,yield strength and tensile strength)are related to the thread connection and the formula type as selected(i.e.,the design formula and the limit formula).