Abstract: Linear circuits typically refer to linear circuit models composed of signal operation units (components and blocks). Since these operation units cover linear operations and calculus operations, and the connections between operation units that determine the operational structure are highly flexible, linear circuits possess powerful computational capabilities and expressive power, making them a bridge between engineering devices and mathematical models. This paper comprehensively organizes the rich knowledge of circuits, proposes the concepts of concrete and abstract models for linear circuits, and outlines the forms and patterns of physical quantities compatible with the abstract circuit model. It refines the overall solution method for linear circuit systems and the classification framework for linear circuits, thereby constructing a knowledge system framework for linear circuits and enhancing the circuit knowledge system.