【Objective】Salicylic acid (SA), a kind of phenolic hormone, could regulate the growth and development of plants, and affect stress resistance of plants. This investigation is to explore effect of extraneous salicylic acid mitigating salt stress on Lolium perenne seedlings.【Method】A pot experiment was carried out, using vermiculite as medium in the pots (20 cm × 15 cm × 9 cm each) for cultivation of Lolium perenne, in greenhouse. The experiment was designed to have two levels of salt stress (0 and 150 mmol L^-1 NaCl) and 5 levels of extraneous SA (0, 0.2, 0.4, 0.6 and 0.8 mmol L^-1) to form 6 treatments, that is treatments CK, S, SSA1, SSA2, SSA3 and SSA4. After germination, Lolium perenne seedlings began to get watered with 50% Hoagland nutrient solution (6.5 ± 0.1 in pH). NaCl solution and salicylic acid were added with the solution on D0 (the 10th day after sowing) when the seedlings was approximately 5 cm in height and then watered once every other day. So the seedlings were watered a total of four times. The seedlings in the treatments were sampled four times on D0, D3, D6 and D9 for systematic analysis of physiological and biochemical indices. 【Result】Results show that application of extraneous salicylic acid, regardless of concentration, significantly mitigated salt stress on Lolium perenne seedlings; relatively improved the seedlings in plant height, and fresh and dry weights of shoot and root; significantly increased the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), thus strengthening the antioxidant enzyme system of the plants; reduced membrane lipid peroxidation and hence damage of the membrane, which was manifested in reduction of cell membrane permeability and malondialdehyde (MDA) content. Compared with Treatment S (150 mmol L^-1 NaCl), Treatment SSA3 was the most prominent in the effect of mitigating salt stress. It increased the plant height of the Lolium perenne seedlings by 43.38%, the fresh and dry weight of the shoot by 37.92% and 31.36%, respectively and the fresh and dry weight of the root by 25.46% and 15.32%, respectively. On D3, SOD activity in the seedlings increased by 17.20%, and on D9, MDA content decreased by 27.60%. 【Conclusion】To sum up, 0.6 mmol L^-1 salicylic acid is the optimal rate among all the concentrations designed to mitigate salt stress of 150 mmol L^-1 NaCl on Lolium perenne seedlings.