Pennisetum sinese Roxb is a kind of forage with high yield and high quality. However, because only the leaves are used as feed, most straw is discarded or burned, causing pollution and resources waste. In this study, a magnetic cellulose adsorbent produced by extracting cellulose from Pennisetum sinese Roxb straw was used to adsorb antibiotic tetracycline (TC) from water and can be easily separated. The physicochemical properties of the obtained cellulose samples were studied. The adsorption process was mediated by multiple mechanisms including intra-particle diffusion, chemical ion exchange, hydrogen bonding, and electrostatic interaction. We determined the optimal pH, contact time, initial TC concentration, and temperature before investigating the effects of humic acid and ionic strength on the adsorption process. Our results demonstrate that the magnetic cellulose is a promising adsorbent for the removal of TC from water and is worth to be studied further to develop real-world implementation strategies.