Carbon Emission Allowance Trading is a market-oriented carbon emission reduction system, and carbon emission environmental impact assessment is a source control system. As a market-oriented incentive tool and a command-and-control administrative regulatory tool respectively, their effective connection is an important rule-of-law path to improve emission reduction efficiency and achieve the "Dual Carbon" goal. At present, China''s carbon emission allowance trading and carbon environmental impact assessment face dilemmas such as poor convergence of laws and regulations, prominent data barriers, and disconnection between environmental impact assessment conclusions and quota allocation, which have made it difficult for the institutional functions to be effectively exerted. Therefore, it is necessary to demonstrate the necessity and feasibility of the connection between the two, analyze the major obstacles in the construction of the convergence mechanism, and construct a legalized convergence path from three dimensions: legal system convergence, data sharing and mutual recognition, and strengthened supervision and guarantee. This will promote the formation of a carbon governance closed loop of "source prevention and control - market incentives - whole-process supervision", and provide theoretical support and practical guidance for enhancing carbon governance capacity.