The origin and evolution of the universe are central questions in modern natural science. The current mainstream theoretical frameworks in related fields are the Standard Model of Particle Physics and the Big Bang theory of cosmology, both of which exhibit significant limitations. The Standard Model fails to incorporate gravitational interactions and includes an extensive array of elementary particle types. The Big Bang theory’s "singularity" hypothesis struggles to explain the initial conditions of the universe, dark matter, dark energy, and the accelerated expansion of the cosmos. This paper proposes a unified theoretical framework — the Great Tao Model, which consists of the Yin-Yang Model of elementary particles and the Theory of Existence Field. The Yin-Yang Model classifies elementary particles into three categories based on charge properties: electron, positron, and subston, and deduces five composite particles (proton, antiproton, neutron, antineutron, neutrino). The Theory of Existence Field posits that charge and mass, as fundamental physical quantities, inherently and continuously diffuse their physical information into surrounding space, forming an "existence field". Elementary particles transmit physical information and interact through their existence fields. Based on the Great Tao Model, this paper systematically elucidates the complete physical picture from the combination of elementary particles to the formation of cosmic structures and provides unified explanations for puzzles such as dark matter, neutrinos, the nature of nuclear forces, the precession of Mercury, and the accelerated expansion of the universe. Philosophically, the model aligns with ancient Chinese Daoist thought, while physically, it embodies theoretical simplicity and unity, making it a potential candidate for a "Theory of Everything".