This book describes unified field theory. The content consists of 3 parts.part Ⅰ: Considering quantization of spacetime and possible fields are derived based on the canonical gauge principle. This includes the gravitational field, and the undiscovered field of spinor gauge connection. The principle of existence of elementary particles, the origin of symmetry, the unification of Boson/Fermion, and the reality of preon are obtained. Lagrangian of the unified field is derived, which includes the modified Dirac equation from field theory. mass-chirality relation is also analyzed.part Ⅱ：From the viewpoint of unified field, the elimination of the divergence difficulty is discussed, then state-constructive field theory is proposed, including some approximate method. Also, the construction and characteristics of field operators are summarized. (ex. projectivity, double completeness, etc.)part Ⅲ：As a part of unified field, the canonical gauge gravitational theory is discussed, based on the results of parts Ⅰ-Ⅱ. By comparing to Einstein theory, the coincidence under spherical symmetry conditions is concluded. From the perspective of quantum cosmology, the resolution of the Big Bang singularity and quantum black holes are analyzed. The cosmological speculations are described in last parts.