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• The superconducting quantum interference working principle of DC SQUID is intuitively interpreted with an interferometric equivalent circuit and the concise dynamic system model. • The interference phenomena inside DC SQUID are simulated and visualized with distributions of the AC current and voltage inside the SQUID to improve the understanding of interferometer mechanism of DC SQUID for both SQUID design and application. Flux modulated static current-voltage characteristics are the basis of DC SQUID being the flux-to-voltage convertor utilized in high-performance magnetic field measurement systems. Those static behaviors are the results of the internal quantum interference between two Josephson junctions. However, the interferometric working principle and the interference phenomena are difficult to be intuitively visualized, either through simulation with conventional models, or through the in-situ measurement inside DC SQUID. Therefore, we redraw the equivalent circuit of DC SQUID in form of the microwave interferometer, and transform it into a concise dynamic system model to study the interferometric mechanism. The double-slit like interference phenomena inside the DC SQUID are visualized through simulations of the AC oscillation current and voltage along the SQUID washer. The concept that DC SQUID is a microwave integrated circuit working as the microwave interferometer rather than a static nonlinear transducer is demonstrated and emphasized. Those concepts help users and designers improve their understandings of quantum interference mechanism of DC SQUID for both circuit design and the practical application system development. [ABSTRACT FROM AUTHOR]