Abstract: 【Objective】Sargassum fermentation liquid was prepared by liquid fermentation of compound microbial agent, so as to investigate application of Sargassum fermentation liquid on rubber seedlings and its effects on cold resistance improvement.【Method】Bacillus, Trichoderma reesei and Aspergillus niger were taken as microbial fermentation agents to conduct liquid fermentation of single strain and compound strain of Sargassum. The experimental study on low temperature stress of rubber seedlings was carried out with compound microbial fermentation broth. The temperature was set at 15℃, and 5 different dosages were set respectively(no fermentation broth, dilution of fermentation broth at 200 times, 400, 600 and 800 times). Compared with rubber seedlings grown at 30℃, pH, alginate content, polysaccharide extraction rate of Sargassum fermentation broth, and biomass, root activity, malondialdehyde(MDA), soluble protein (SP) and antioxidant enzyme content of rubber seedlings were measured.【Result】 In the fermentation process of Sargassum compound microbial agent, pH values of all treatments decreased first and then increased, and alginic acid content of compound microbial agent was slightly higher than that of single strain. In terms of polysaccharide extraction rate, the compound bacterial agent treatment group was significantly higher than the single strain treatment group and the extraction rates of Bacillus and T. reesei were the highest, 14.08%. In the experiment of low temperature stress, the biomass of rubber seedlings decreased, and the root activity of rubber seedlings treated with Sargassum fermentation broth increased. The root activity of Sargassum fermentation broth diluted at 600 times was the largest, which was 0.051 mg/(g·h). The content of MDA and SP in rubber seedlings increased under low temperature stress. The increase of MDA content in Sargassum diluted at 600 times was the smallest, and the SP content increased by 22%. Under low temperature condition, the peroxidase(POD) activity of the other treatments decreased, except for the treatment of Sargassum fermentation broth diluted at 200 times. Superoxide dismutase(SOD) activity of Sargassum fermentation broth diluted at 600 times was the highest among the 3 antioxidant enzymes, and catalase(CAT) enzyme activity was the highest when the fermentation liquid of Sargassum was diluted at 400 times.【Conclusion】 The degradation effects of compound microbial agent is significantly better than that of single bacterial agent. The synergistic fermentation of Sargassum by Bacillus and T. reesei are the best. Diluting the Sargassum fermentation broth at 600 times can effectively reduce damage of low temperature to rubber seedlings and improve their stress resistance.