Currently available data on density of hemp are all specific values, and their differences are obvious, which could bring trouble to the related products’ development and actual production. Therefore, provide accurate density values conducive to better achieve the development and use of hemp fiber related products. This paper mainly analysis the relevancy between hemp bast fibers’ chemical compositions and its density after degumming, and draw a conclusion that the density of hemp fiber is not a fixed value but a range of variation. The density will be changed when chemical composition contents in different hemp fiber are different. Which chemical composition that affected the density most is cellulose content, followed by pectin content, and than, the lignin content and hemi cellulose content.