an innovative algorithm for computer-aided circuit design is presented in this paper. The algorithm is applied to "relative" circuits during optimal circuit design process to reduce circuit simulation time. The new concepts of "relative" circuits, fundamental circuit, derivative circuit, and delta circuit, are introduced. A practical implementation approach is developed with a Spice simulator, accordingly. The algorithm can be adapted to statistical designs or optimal designs. An example is given to prove the correctness and efficiency of the algorithm.