["Review of Development Economics, EarlyView. ", "\nABSTRACT\nAs economic globalization shifts toward regionalization, complex knowledge becomes increasingly crucial. Burgeoning literature begins to explore how complex knowledge facilitates economies. Given the representativeness of the “Belt and Road” Initiative in world economic regionalization, we extend this discussion within the countries involved, and make several distinctions. First, by combining the Fitness and Complexity (FC) Algorithm and the Matrix‐Estimation exercise in the bipartite network, we develop a more comprehensive and effective method to measure knowledge complexity based on the similarity and specialization of patents' output structure. Second, by employing the Instrument Variable Fixed Effect Quantile Regression (IV‐FEQR), we investigate the economic effects of complex knowledge production while considering heterogeneity and endogeneity issues. Our findings indicate that increasing knowledge complexity significantly promotes a country's economic growth, a result that remains robust across various checks. The benchmark result can be explained theoretically well through the macro‐ and micro‐level driving forces, which are also empirically identified. Heterogeneity results further reveal that the promotion effect varies across regions and “expirations.” In addition, the results of moderating effect regressions also emphasize the positive role of the “Belt and Road” Initiative as a moderator; we also find that its interaction with external factors exhibits both a leveraging effect and a mitigating effect. Our analysis provides practical insights for measuring knowledge complexity and offers important policy implications for boosting economic growth amid current geopolitical tensions.\n"]