Porous cellulose aerogel materials are attracting increasing interest due to their promising potential in multiple fields. In this paper, highly porous and mechanically strong cellulose aerogels were successfully prepared from microcrystalline cellulose and dissolving pulp in ionic liquid BmimCl via a sol–gel polymerization method. The surface morphology and physical properties were characterized by scanning electron microscopy, X-ray diffraction, and compression tests, etc. The differences in microstructure, crystalline structure, and mechanical performance of these two kinds of cellulose aerogels were studied and compared. Moreover, the two cellulose aerogels were used as adsorbents to remove dye, oil, and organic solvents. The kinetics and equilibrium capacity were investigated. Results indicate that the cellulose aerogels with high degrees of polymerization have much better mechanical strength and adsorption properties than the cellulose aerogels with low degrees of polymerization.