Carbon emission and climate change are of the most emergent challenges faced by human beings. Most current literatures focused on technologies of low carbon,energy - saving,carbon emission measurement,carbon information disclosure,etc. Seldom researches concerned the executive force of climate activities from a perspective of organizational management effectiveness. An index system of effectiveness assessment was constructed according to the carbon management process in this research. Combining with the cloud theory,the management effectiveness evaluation method and cloud graph were proposed to cope with fuzziness and randomness contained in linguistic concepts. The simulation example further indicated that the effectiveness assessment result calculated by cloud theory method conformed to normal distribution law and the assessment method could be simulated to calculate a great quantity of assessment information from a small quantity of information status,and disclose the result of organizational effectiveness of climate activity in carbon emission field more clearly.