In the context of global climate change and carbon-neutrality goals, carbon taxes and carbon tariffs have become key policy tools for regulating corporate emissions. However, most existing studies examine these policies in isolation and overlook firms’ behavioral responses under their joint implementation, especially with product heterogeneity. This study analyzes production and emission-reduction decisions of two-country manufacturers under carbon taxation and further investigates corporate behavior and social welfare outcomes when both carbon taxes and carbon tariffs are imposed. The results show that carbon taxes enhance emission-reduction efforts, though with diminishing marginal effects. Moderate carbon tariffs further motivate exporting firms to reduce emissions, while overly high tariffs may induce market exit, particularly for high-quality manufacturers. Consumer preferences also interact with policy effects: stronger preferences for high-quality products encourage firms to expand domestic markets and increase green investments, whereas weaker preferences shift focus toward exports. Social welfare responds asymmetrically, moderate tariffs improve environmental performance, while excessive tariffs lead to trade distortions and welfare losses. Overall, this study highlights nonlinear and heterogeneous firm responses under combined carbon policies, offering insights for policy design and corporate strategy.