Digitalization supported by ICT capital is a core weapon for decoupling economic growth from carbon emissions. This research innovatively calculates ICT capital in China from 2001 to 2018 and explores how ICT capital affects carbon emission efficiency and its spatial spillover effects from a digital investment perspective. The empirical results prove that ICT capital contributes to improvement of carbon emission efficiency, pure technical efficiency, scale efficiency and technological progress. Furthermore, interestingly, ICT communication capital was found to have the strongest effect on improving carbon emission efficiency, while ICT hardware capital and software capital have a weaker effect. The spatial effect demonstrates that ICT capital not only helps improve the local carbon emission efficiency but also has spatial spillovers to the surrounding areas and has the most prominent effect on the carbon emission efficiency of the central region. The mediation tests illustrate that ICT capital improves carbon emission efficiency by promoting technological innovation, alleviating industrial structure distortions, enhancing resource allocation efficiency and accelerating human capital accumulation. These findings have important policy guiding significance for the region to stimulate the potential of ICT capital and facilitate the low-carbon transformation of the economy. © 2022 Elsevier B.V.