The identification of justifiable self-defense has long been mired in a disconnect between "doctrinal complexity" and "public sense of justice." Although modern criminal jurisprudence has constructed a comprehensive theoretical framework—encompassing unlawful infringement, defensive intent, and necessary limits—its highly abstract terminology and complex balancing of legal interests have not only increased the risk of judicial discretion but also significantly raised the social cost of legal interpretation. In the face of urgent public demand for justice in "counter-killing" cases, traditional vague reasoning can no longer provide stable legal expectations. This article proposes a quantitative determination model based on Statutory Penalty Differentials by integrating sentencing penalties with the principle of balancing legal interests. The model simplifies complex defense determinations into an equivalence calculation between "infringement intensity" and "defense level." Through fitting and deduction of a series of landmark cases, the results derived from this model are highly consistent with the rulings in official guiding cases. This demonstrates that the quantitative model possesses strong empirical value in simplifying legal interpretation and unifying judicial standards, providing an intuitive benchmark for the public to understand the law.