Abstract: Chlorophyll content, nitrate reductase activity, photosynthetic characteristics and grain-filling processes of winter wheat were investigated in a field experiment for the effects and mechanisms of three plant polysaccharide compound agents P1 (plant polysaccharide extracted from natural plant and marine biological resources), P2 (plant polysaccharide/5-aminolevulinic acid) and P3(plant polysaccharide/5-aminolevulinic acid/dimethylpiperidinium chloride). The effects of agents on the growth and grain yield of winter wheat after foliage spraying at early flowering stage were determined. The results indicated that the agents increased SPAD values in flag and top second leaves. It delayed the decrease of chlorophyll content as plants development. Net photosynthetic rates of flag leaves increased by 8.7%~17.4%. Increases in SPAD and photosynthetic rate under P1 and P2 treatments were larger than those under P3 treatment. Furthermore, nitrate reductase activities increased under P1 and P2 treatments and water use efficiency (WUE) of flag leaves increased in excess of 10%. Under the compound agent treatments, the period until maximum grain-filling rate shortened by 1.3~4.2 d. Mean grain-filling rates increased by over 6% under P1 and P2 treatments. While no obvious change was noted in mean grain-filling rate under P3 treatment, grain-filling duration lengthened by 1.0 d. Whereas there was no significant change in spike number, grain number per spike and kilo-grain weight improved. Grain yield of winter wheat treated with compound agents increased by over 8% compared to the control treatment. Chlorophyll content increase, leaf senescence delay, and enhanced photosynthetic capacity and grain-filling processes improved winter wheat yield under polysaccharide compound agent treatments.