Abstract: The complex impedance network is different from the pure resistance network，and the change of the circuit element has a great influence on the equivalent complex impedance. In this paper，the equivalent complex impedance formula of the two terminal RC complex impedance network is studied by using the method of establishing the model of nonlinear difference equation. According to the different conditions of the potential，the universal formula of the equivalent complex impedance of RC ladder network under different conditions is studied by using the complex analysis method，and the equivalent capacitance formula of pure capacitance network is obtained naturally.

Key words: RC ladder network, nonlinear difference equation, equivalent complex impedance, universal formula