Against the backdrop of profound adjustments in the global distribution of factor income, how China can optimize its factor income distribution while deeply participating in global value chains has become a critical practical challenge for advancing the strategy of common prosperity. This paper empirically examines the mechanisms through which external demand shocks affect factor income distribution at the firm level. The findings reveal that external demand shocks significantly alter the patterns of factor income distribution, manifesting specifically as a substantial decline in labor income share. This redistributive effect is primarily realized through the innovation effect and the value-chain upgrading effect. Heterogeneity analysis demonstrates that the inhibitory effect of external demand shocks on factor income distribution mainly occurs in high-productivity firms, large-scale firms, high R&D intensity firms, and high value-chain position firms. The findings not only provide empirical support for deepening the theory of factor income distribution under the conditions of the open economy, but also offer policy insights for coordinating the construction of a strong trading nation with the achievement of common prosperity in the new era. It is necessary to promote the rationalization of factor income distribution through comprehensive measures such as improving income redistribution mechanisms, strengthening labor skill training, and optimizing industrial upgrading paths while fostering foreign trade development, thereby ensuring that the dividends of globalization better benefit the broad working population.