The invention belongs to the technical field of plant growth conditioning agents, and relates to a plant salt resisting conditioning agent. The plant salt resisting conditioning agent is prepared from porphyra polysaccharides with the concentration of 100-1,000 mg/L, salicylic acid with the concentration of 0 mg/L or 100-200 mg/L, brassinolide with the concentration of 0 mg/L or 0.01-0.1 mg/L, glycine betaine with the concentration of 0 mg/L or 100-1,000 mg/L, spermidine with the concentration of 0 mg/L or 10-100 mg/L, a surfactant with the concentration of 0 mg/L or 1,000-20,000 mg/L and water, wherein the water serves as a solvent, and low-molecular-weight porphyra polysaccharides with the molecular weight of 1 k-50 k Da are adopted as the porphyra polysaccharides. Accordingly, novel application of the porphyra polysaccharides is supplied, and the porphyra polysaccharides can be used for preparing the plant salt resisting conditioning agent; meanwhile, by compounding the porphyra polysaccharides with the biological source induced resisting substances such as salicylic acid, brassinolide, glycine betaine and spermidine to prepare the salt resisting conditioning agent, the comprehensive resistance of plants on salt stress can be improved, and normal growth and development of the plants are guaranteed; according to the salt resisting conditioning agent, the components are simple, the raw materials are easy to obtain, the cost is low, the effect is significant, and environmental friendliness is achieved.