The integration of economies always attracts much attention from policymakers and researchers. This paper introduces a novel approach to evaluate potential economic and environmental gains from integrating economies. Based on aggregate production technology and directional distance functions, we regard all decision-making units as a whole, allowing free resource reallocation among units. The level of resource misallocation is identified by a structural measure, which is obtained by the difference between overall potential improvement and individual technical inefficiency. Taking China as an empirical example, possible economic output expansions are estimated at 43.2% and 10.1% under convex and nonconvex production technologies, respectively; potential pollution reductions are around 28.4% and 5.1% under convex and nonconvex production technologies, respectively. A significant disparity of structural inefficiencies is detected, indicating a high level of resource misallocation in China. Economic cooperation is vital to promote potential green gains for all provinces in China.