Lack of policy guidance in low-carbon technology innovation poses dual externalities in terms of technology and environ-ment,which severely inhibits the vitality of enterprises in low-carbon technology innovation.To explore whether the implementation of low-carbon development and intellectual property protection policies effectively alleviates the dual externalities of low-carbon technology innovation,this study examined a sample of high-carbon emission enterprises listed on A-share markets and major cities across China from 2007 to 2021,by using the Difference-in-Differences(DID)and difference-in-differences-in-differences(DDD)methods.The findings are as follows:(1)Both the low-carbon city pilot policy and the intellectual property demonstration city policy effectively alle-viate the dual externalities of low-carbon technology innovation at both the city and enterprise levels.This conclusion remains valid af-ter addressing endogeneity and undergoing multiple robustness tests.Further heterogeneity studies revealed that these two policies have a better effect on promoting low-carbon technology innovation in enterprises located east of the"Hu Line",non-state-owned enterpri-ses,lightly polluting enterprises,and startups.(2)The mechanism tests indicated that low-carbon development and intellectual prop-erty protection policies alleviate the dual externalities of low-carbon technology innovation by enhancing enterprises'environmental at-tention and innovation attention,respectively.(3)The results of policy interaction tests showed that there is a synergistic effect between the two policies,and the effectiveness of this synergy is greater than the individual effects of each policy.This research will deepen the un-derstanding of enterprise competition theory in the context of low-carbon development,expand the research boundaries of externality issues in low-carbon technology innovation,explore the research ideas and methods for the synergistic effects of multiple policies,and provide the-oretical references and empirical evidence for the construction and improvement of relevant policy systems in the future.