Studying the synergy effect of pollution reduction and carbon emission reduction when the “Broadband China” strategy is superimposed with the pilot policies of low-carbon cities is of vital importance for achieving the “dual carbon” goals. Based on the panel data of 284 prefecture-level and above cities in China from 2006 to 2021, this paper empirically studies the impact of the “Broadband China” strategy and the dual pilot policy of low-carbon cities on the synergy of pollution reduction and carbon emission reduction by using methods such as the multi-period difference-in-differences method and the spatial difference-in-differences method. The study finds that:1） The dual-pilot policy can significantly enhance the synergy effect of pollution reduction and carbon reduction, and the enhancement effect is stronger than that of single-pilot policy. 2） The dual-pilot policies can enhance synergies in reducing pollution and carbon emissions by promoting innovative and improved green technology innovations. 3）The dual-pilot policy will not only enhance the synergy effect of pollution and carbon reduction in the region, but also in the neighbouring cities.4）The synergy effect of pollution reduction and carbon emission reduction in cities with high administrative levels, resource-based cities, cities with high economic development and non-old industrial cities is more strongly influenced by the dual pilot policy. （5）Becoming a low-carbon city before becoming a “Broadband China” demonstration city has a greater impact on the synergistic effects of reducing pollution and carbon emissions. The study suggests that the huge effect released by the superimposition of policies should be emphasized, and the potential of green technological innovation to empower the green development of cities should be brought into play. While carrying out pollution reduction and carbon emission reduction work in accordance with local conditions, the synergy among cities should be fully exerted.