—On optimizing circuit trajectories, i.e. continuous paths of circuit parameters, the paper presents an auxiliary network approach, which utilizes Pontryagin’s Minimum Principle. Based on a set of circuit element correspondence rules, the introduced approach establishes an auxiliary network for a given circuit to be optimized, then circuit trajectories are optimized in a process of simulating the given circuit and the auxiliary network. The auxiliary network approach facilitates establishing analytic models in designing high-performance circuits that require fine tuning circuit trajectories. The paper details the theoretical framework of auxiliary network, and provides practical examples of its application in adiabatic circuit design.