Abstract: The bearing capacity of compression bars is mostly controlled by stability rather than strength. It is the main goal to improve the stable bearing capacity of the compression members when they are reinforced. Outer sleeve reinforcement is a kind of method with definite load condition and convenient construction, and has been widely used. Rigid prestressed strut reinforcement is also a method to reduce the compressive stress of compression bar. In the paper, the lateral deformation between the steel sleeve and the reinforced compression bar was kept in harmony. The critical value of the stability bearing capacity of the compression bar was obtained by using the condition that the release of compressive strain energy was equal to the absorption of bending strain energy in the case of instability. The formula was also suitable for the design and calculation of the reinforcement with rigid prestressed strut. An example of large deformation geometric nonlinear instability was calculated by ANSYS and the critical values of stability load under four different loading conditions were obtained. The difference from the theoretical analysis value was less than 1%, which verified the correctness of the theoretical value in the paper, and also verified that the outer sleeve and compression bar could meet the requirements of consistent deformation through several node limits.