Recently, blockchain has been increasingly applied to low‐carbon supply chains, enabling consumers to track production process of low‐carbon products, thereby improving brand awareness and expanding the market. However, do the operation and construction costs of blockchain come at the expense of squeezing resources originally allocated for research and development (R&D) of carbon emission reduction (CER) or reducing firms profits? Given the varying capacities of different types of firms to bear the costs of blockchain in the process of R&D of CER, this paper considers two categories of firms, superior brand firms and inferior brand firms, and studies the impact of blockchain usage on CER and profits. Research shows that the usage of blockchain is not necessarily beneficial to CER and profits enhancement. Consumers' trust and low‐carbon preference, brand awareness, blockchain operation and construction costs, and R&D difficulty of CER are key factors. Superior brand firms can improve CER level and profits through blockchain when R&D difficulty is low and consumers' trust is high or when R&D difficulty is high but consumers' low‐carbon preferences and brand awareness are high. Inferior brand firms can improve CER level and profits through blockchain when R&D difficulty is low and consumers' trust is high or when R&D difficulty is high but brand awareness is low. This study provides strategic insights for brand firms considering the usage of blockchain in their CER initiatives, highlighting the importance of aligning blockchain integration with firm‐specific characteristics and market conditions to achieve both environmental and profit objectives.