The invention relates to an addition agent for nicosulfuron oil-based suspension concentrate. The addition agent is prepared by the following materials, by weight: 10-60% of nonylphenol polyoxyethylene ether, 10-50% of castor oil polyoxy ethyl ether, 5-20% of fatty alcohol polyoxy ethyl ether, 5-25% of alkyl benzene sulfonic acid and 5-40% of solvent oil. The invention further relates to nicosulfuron oil-based suspension concentrate. The novel addition agent for the nicosulfuron oil-based suspension concentrate is good in dispersibility and stable in performance, and can not only be used for preparing the nicosulfuron oil-based suspension concentrate of 4%, but also be used for preparing the nicosulfuron oil-based suspension concentrate of 20%. Active ingredients in the preparation are improved after the nicosulfuron oil-based suspension concentrate with a high concentration is prepared, using quantities of organic solvents and the addition agent are reduced, the pollution to the environment is reduced, and the cost can be reduced. Epoxidized soybean oil is further added to serve as a stabilizing agent, reduces decomposition rate of nicosulfuron, and maintains pesticide effect.