Psychology has long been mired in a “pre-paradigmatic” state of fragmentation, with its mainstream schools (psychoanalysis, CBT, humanistic psychology, etc.) built upon mutually incompatible foundational assumptions. This situation resembles the parable of “the blind men and the elephant,” leading to dual crises in both theory and clinical practice. To fundamentally transcend this historical impasse, this paper undertakes a radical paradigm reset: it introduces a more foundational Systemic Ontology as a metaframework and, through rigorous top-down deduction, constructs for the first time a unified axiomatic system for psychology. We first establish two meta-axioms that constitute the bedrock of existence (the Principle of Self-Organizing Dynamical Trend and the Principle of Systemic Constraint) and derive from them five core axioms. Based on this foundation, we strictly deduce three psychology-specific theorems: the Theorem of Mental Hierarchical Conflict (which uniformly defines psychological suffering as internal imbalance within the tri-level conscious system), the Theorem of Cognitive Framework Fitness (which proposes a quantifiable health formula: Fitness = (D × E)/(R + ε)), and the Theorem of Noetic Niche Interaction (which interprets health by situating the individual within the social network). Using this theorem system as an operational framework, we reinterpret seven major schools of psychology, demonstrating that each is a specific application of this metatheory at different systemic levels, addressing different conflict types and intervention foci. Consequently, we construct a novel, multi-dimensional system-diagnosis-based, hierarchical intervention protocol. The contribution of this study lies not only in providing psychology with a logically coherent, universally explanatory metatheoretical foundation but also in advancing it from a descriptive “collection of schools” to a normative science with unified principles, operationalizable measurements, and a testable research program.