Guided　by　the　concept　related　to　sustainable　development,　we　investigate　the　effects　related　to　the　synergistic　agglomeration　development　of　productive　service　and　manufacturing　industries　on　regional　green　development,　which　is　also　an　important　path　for　promoting　the　global　sustainable　development　process　and　achieving　carbon　neutrality　goals.　Using　the　panel　data　of　285　prefecture-level　cities　in　China　from　2011　to　2020　as　the　basis　of　our　study,　we　focus　on　the　impact　of　industrial　synergistic　agglomeration　on　the　efficiency　of　regional　green　development　and　the　mediating　influence　of　technological　innovation.　Results　show　that　(1)　industrial　synergistic　agglomeration　positively　contributes　to　the　improvement　of　regional　green　development　efficiency　level　and　is　significantly　positive　at　the　5%　level,　(2)　technological　innovation　plays　a　mediating　role　in　the　process　of　promoting　regional　green　development　efficiency　through　industrial　synergistic　agglomeration　and　can　better　realise　the　green　development　effect　of　industrial　synergistic　agglomeration,　(3)　results　of　the　threshold　effect　test　show　the　nonlinear　effect　of　industrial　synergistic　agglomeration　on　regional　green　development　efficiency　with　a　single　threshold　value　of　3.2397,　and　(4)　the　effect　of　industrial　synergistic　agglomeration　on　regional　green　development　efficiency　shows　significant　variability　under　different　geographical　locations,　city　scales,　and　resource　endowment　conditions.　On　the　basis　of　these　findings,　we　propose　corresponding　policy　recommendations　for　improving　the　quality　of　inter-regional　industrial　synergistic　agglomeration　and　formulating　differentiated　policy　guidelines　to　help　regions　achieve　long-term　sustainable　development.