The invention provides a method for quickly starting nitrosification through preposed anaerobic stirring, and belongs to the field of urban sewage treatment and reutilization. The method for quickly starting the nitrosification in an SBR reactor by a preposed anaerobic stirring strategy in the reaction early stage comprises the following steps: at first, nitrification sludge of an urban sewage plant is inoculated, the concentration of influent ammonia nitrogen is controlled to 120 plus or minus 15 mg/L, dissolved oxygen is stabled to 0.2 to 0.5 mg/L through controlling the aeration quantity, and the nitrosification is successfully started for 20 days and 60 periods by the preposed anaerobic stirring. Under the condition, the nitrosification is in operation stably for 15 days and 30 periods, and the nitrosification rate reaches more than 90 percent always. The concentration of the influent ammonia nitrogen is changed to 35 plus or minus 5 mg/L, the nitrosification rate reaches more than 90 percent always, and the long-term stable operation of the nitrosification is maintained. The method solves the traditional thought that for a long time, free ammonia and low dissolved oxygen are simply used for starting the nitrosification, and enables the starting of the nitrosification to be quicker, more convenient and more efficient.