Whether cultural distance raises or lowers post-acquisition innovation performance remains unsettled in international business research. We use panel data on cross-border M&A events completed by Chinese A-share listed firms and estimate pooled OLS models that test an inverted-U effect of cultural distance on post-acquisition innovation and the moderating role of R&D intensity. Cultural distance and innovation performance show a significant inverted-U relationship, but this main effect loses significance once industry fixed effects are controlled; its identification depends on systematic differences in target-country cultural distance across industries. R&D intensity has a structurally robust moderating effect on the inverted U: it strengthens the positive slope at low cultural distance and deepens the negative slope at high cultural distance, and this moderation stays significant under industry fixed effects and the Heckman two-stage correction. The paper makes two contributions. First, the moderating effect of R&D shows that the marginal return to absorptive capacity reverses direction as cultural distance rises, which marks the boundary of absorptive-capacity theory in cross-cultural settings. Second, the sensitivity of the inverted-U main effect to model specification is a caution for future non-linear empirical work: robust identification of non-linear effects requires careful attention to unobserved heterogeneity at the industry and firm levels.