Infra-red spectrum and ultraviolet absorption spectrum were used to study the structure characteristics of the sodium lignosulphonate from black liquor of poplar tree，straw，bamboo and bagasse.Gel chromatography analysis showed that the weight average molecular mass of poplar and bamboo lignosulphonates were 5306 and 5520 respectively，higher than those of straw and bagasse lignosulphonates，which were 2594 and 3596 respectively.Chemical titration measurements showed that the sulfonic group content of poplar lignosulphonate was 1.15 mmol·g-1，which was lower than that of straw and bamboo lignosulphonates，but higher than that of bagasse lignosulphonate，and the phenolic hydroxyl group content of poplar lignosulphonate was 1.01 mmol·g-1，which was higher than that of other three lignosulphonates.The four sodium lignosulphonates were used as additives of coal water slurry and the effect of the structure characteristics of different lignosulphonates on the viscosity reduction of coal water slurry was investigated.The results showed that the raw material of lignosulphonate，relative molecular weight distribution and sulfonic group content were the main affecting factors.