The invention discloses an SBR (sequencing batch reactor) nitrosation quick start method, and belongs to the field of urban sewage treatment and resource recycling. Aiming at the problems that AOB (Ammonia Oxidizing Bacteria) and NOB (Nitrite Oxidizing Bacteria) are similar in growth characteristics and AOB are difficult to separate and screen, returned nitration sludge in a sewage treatment plant is inoculated in an SBR reactor, the inflow ammonia nitrogen concentration is controlled at 300-500mg/L, the aeration quantity is controlled so that the concentration of dissolved oxygen is 0.2-0.5mg/L, the aeration time is controlled so that the ammoxidation rate is controlled at 30-50%, sodium hydrogen carbonate is added to regulate and control pH at 7.70-8.20, and the outflow nitrosation rate that is the ratio of nitrite accumulated by reaction and the sum of accumulated nitrite and nitrate is calculated by maintaining the conditions. The nitrosation rate reaches more than 90% after 4 days and 8 cycles, and the nitrosation rate is always more than 90% after 7 days and 14 cycles, so that the nitrosation is successively started.