In order to identify the DC-DC converter system behavior with different feedback coefficient k, we propose a method, which adopts the ideas of limit and the information about entropy to estimate the DC-DC converter nonlinear behavior by considering the characteristics that the stability of the system in a state of cycle and when the system is in chaos will not be repeated. This method analyses the entropy of the system in periodic and chaotic states and can quantify the period-doubling and chaos behaviors in DC-DC converters. In this paper, we simulate the first-order voltage feedback DCM Boost converter and DCM Buck converter. Results indicate that, according to the proposed information entropy, the bifurcation point, cycle number, and the location of the chaos can be accurately reflected. The above method improves the theory and method of the converter nonlinear dynamics analysis.