This paper comprehensively studied volume growth, carbon storage, and carbon fixation of poplar. Also the author researched economic benefit of crops on the poplar-crop agroforestry system with three different planting densities in northern Anhui Province. The result showed that relationships among volume growth rate, carbon storage and carbon fixation were significant. However, the increase of total Carbon storage had no significant relationship with the increase in individual poplar. Over three different planting spacing such as 4m×6m, 3m×8m, 2m×6m of poplar, the planting spacing of 3m×8m gained the highest comprehensive benefit and made a great improvement on carbon storage of individual poplar than other two patterns.