Abstract: A relatively simple method for calculating three-layer shells was proposed for the complex problem of three-layer shell calculation, named as the method of stiffness equivalence, which was based on the research achievement of general thin-shell theory and could directly use those theoretical formulas. Itcould not only cut down the labor resource, but also reserve the precision of the calculation by using this method. After analyzing the characteristics of those adopted formulas and using the principle of stiffness equivalence, the calculating process was given out; the formulas of the equivalent elastic module and the equivalent thickness were deduced. In the following example, The equivalent elastic module and the equivalent thickness were taken into the formulas of the general thin-shell theory, and the result of the three-layer column shell based on the elastic condition was obtained, which was further verified by numerical calculation. The calculating results show that the method of stiffness equivalence can be used for the calculation of three-layer thin shells.