Abstract: This paper presents a comparison study on the existing common methods for calculation of stiffener ring buckling of embedded steel penstocks under external pressure. The results indicate that the critical external pressure of stiffener ring obtained from equation (B16) in the design codes DL/T 5141—2001 is conservative. Equation (30) in the appendix of the codes is an incorrect expression of Svoisky's method and it may lead to a too large or even wrong estimate for the critical pressure. Moreover, Jacobsen's method not only overcomes the limitation in the adaptation range of Amstutz's method, but avoids the shortage of Svoisky's method that fails to consider the external pressure of shell beyond the equivalent flange. Thus Jacobsen's method is recommended and an effective calculation thought for solving the Jacobsen's formulas is given.