In April 2025, the United States launched a new round of global tax restructuring, promoting a "reciprocal taxation" mechanism toward multiple trading partners, which quickly triggered countermeasures from China. The institutional reshaping of global tax rules has thus emerged as a novel external shock, intensifying international capital's arbitrage incentives and profit-seeking behavior in the short term and inducing cyclical mismatches and structural shifts in cross-border capital flows. Compared with traditional analytical frameworks based on interest rate differentials and exchange rate fluctuations, such institutional shocks are more likely to generate nonlinear responses through changes in policy expectations and amplified market sentiment, making their dynamic evolution difficult to capture using conventional methods. Against this background, the asymmetric adjustment mechanisms of China's short-term cross-border capital flows under global tax competition was examined. Using quarterly data from 2008 to 2024, a multiple-threshold regression model and introduce generative artificial intelligence was constructed to perform semantic modeling of policy texts, thereby developing a tax policy semantic intensity index (TPSI). The results show that global tax shocks significantly alter the response structure of capital flows to interest rate and exchange rate expectations, exhibiting clear regime shifts and asymmetric effects. The TPSI demonstrates strong leading properties in identifying the direction of capital sentiment and flow dynamics, effectively compensating for the lag of traditional variables in capturing policy expectation changes. Moreover, under high semantic intensity regimes, the marginal effectiveness of existing macroprudential tools weakens, increasing the risk of "high-frequency decoupling" in short-term capital flows. Accordingly, it proposes establishing a cross-border capital early-warning system based on semantic expectation identification, proactively enhancing capital flow governance, and actively participating in the reconstruction of global tax rules to strengthen China's institutional resilience and safeguard its tax sovereignty within the international financial system.