Based on the the composition of natural plant fibers, the pretreatment methods of different kinds of plant fiber were introduced, and the modification methods and adsorption mechanism were analyzed. The shortcomings of the existing research and the improvement direction were discussed. The analysis shows that waste natural plant fibers are usually used as the matrix of cellulose-based adsorbents. However, the untreated fiber has strong hydrophobicity and high crystallinity, which are not conducive to adsorb heavy metals rapidly and completely. Acid treatment can protonate the adsorption sites. The lignin can be removed by alkali treatment. The surface impurities can be removed by organic solvent. Carboxyl groups are introduced by esterification modification. Aldehyde groups, ketone groups, carboxyl groups and enol groups are introduced by oxidation modification. Functional groups such as amino, amide, and sulfonic acid groups are introduced by graft modification. Surface complexation and electrostatic attraction, which have selective adsorption properties, are the main mechanism of the adsorption of heavy metals. In order to improve the modification effect of cellulose, the corresponding pretreatment and modification methods should be selected according to different fiber composition and adsorption requirements of heavy metals.