•A benchmark of cylindrical shell for investigating the effect to KDF from pure geometric imperfections is provided.•The Fourier series method is compared with the scatter points method for computation efficiency and prediction accuracy.•Guidance in dimensional tolerance is given for maximizing the load-carry capacity of cylindrical shells in manufacturing. Imperfections from manufacturing process can cause a scattered reduction of the load-carrying capacity or buckling load of axially compressed cylindrical shell structures. To isolate the influence of geometric imperfections from other imperfections such as welding, a sub-scaled, integrally manufactured cylindrical shell with small-amplitude geometric imperfection was manufactured, analyzed and tested in this study. A test facility and measurement system (including imperfection measurement and buckling test) were constructed. Finite element (FA) numerical procedure for predicting the buckling load was developed. Results indicate that the buckling load predicted by the FE analysis is very close to that from the test. Knockdown factor (KDF) is discussed with reference to the NASA design document. Furthermore, the influence of pure geometric imperfections including imperfection component and amplitude on the buckling behavior is discussed based on Fourier series method. Some guidance for the dimensional tolerance in manufacturing process relating to the load-carrying capacity of thin-walled structures is provided.