The solutions of dynamical system expressed with nonlinear differential equation usually is shown by using time function () u t. But this is not unique mode, when particularly () u t cannot be solved. In the modern theory of circuit and system, we can select three dynamical variables in the nonlinear system to constitute 3-dimension phase space. The mutual nonlinear relation among three dynamical variables can be described by a bounded space curve. This is 3-dimension phase portrait. The nonlinear dynamical systems of regarding 3 N > variation may constitute N-dimension Euclidean space. The bounded space curve cannot be represented by concretely explicit parametric form in math. It cannot be solved analytically by human. However, the graphic solution can be plotted by numerical simulation. If the bounded space curve is non-periodic in simulation interval, this is orbital chaos of continuous time system. This paper researches the produce and property of chaos by means of the analysis method of frequency domain and theorem of power balance. We prove that the second order differential circuit which is constituted by mixing of multi-excited source with different frequency also can produce chaos.