Effect of paclobutrazol (PP333) on the extension and root characteristics of Lolium perenne. L was investigated with a pot experiment. The results showed that, plant growth, shoot extension, shoot biomass growth and vertical growth of root of Lolium perenne. L were all inhibited, while the tillering was enhanced at the PP333 concentration changing from 100 to 1 900 mg·L-1. Less obvious inhibition of paclobutrazol on shoot biomass growth, maximum extension distance and root growth, plant height, plant coverage was observed at the PP333 concentration larger than 400, 700, 1 000 mg·L-1 and 1 300 mg·L-1, respectively. Tillering number, root surface area, volume and biomass of Lolium perenne. L first increased then decreased as the concentration of paclobutrazol increased, all reached their maximum values at the concentration of 1 300 mg·L-1. Shoot extension decreased as the concentration of paclobutrazol increased, slow decrease occurred as the concentration was larger than 700 mg·L-1, the extension of root was first improved then inhibited by paclobutrazol as its concentration increased, 1 300 mg·L-1 is the optimal concentration for root extension of the plant, the overall expansibility of the Lolium perenne. L decreased with increasing of paclobutrazol concentration.