The theory of structural stability is both an important and a difficult subject, whose main field of application is found in the design of thin wall lightweight structures and shells. It is unavoidable to employ nonlinear model and to use finite element numerical method in order to obtain the critical load under the action of which the instability of structures will occur. Thus, it becomes very important how to simplify such a nonlinear problem that appears in instability analysis. In this paper, an improvement on previous nonlinear buckling analysis is proposed, in which the emphasis is on the shortcut of calculation of pre-buckling fundamental path. The nonlinear equation used to solve the displacement vector is translated into the linear one to solve the load factor by means of the concept of energy conservation. The detailed procedure to calculate the nonlinear buckling load is presented and two simple examples are also shown as the application of suggested method. The theoretical analysing and numerical examples show that the suggested method is valid for predicting the nonlinear critical loads of structures.