Abstract: In order to explore the factors affecting the process start-up of anaerobic moving bed biofilm reactor at low temperature and obtain the optimal start-up process parameters, an experimental platform was established on the basis of selecting K3 filler packing as the reactor filler with natural inoculation process. Under different levels of filling rate, reflux ratio and hydraulic retention time at the water temperature of 8-12 ℃, and different operating conditions the operating effects of the reactor were obtained by studying on the treatment effect of the reactor during film hanging start-up on chemical oxygen demand, NH₃-H and total phosphorus in sewage. The growth rate of biofilm under different operating conditions was obtained by studying on the mass changes of biofilm on the filler in the reactor. By studying the gas production rates of the biofilm, the total specific respiratory rates and endogenous sources specific respiratory rates of the biofilm in the reactor under different operating conditions were obtained. By comparing the operating efficiency, the activity and respiratory rates of the biofilm, the optimal process parameters for the start-up of the A/MBBR with natural inoculation process at 8-12 ℃ were obtained: the filling rate was 40%, the reflux ratio was 20%, and the hydraulic retention time was 8 h. Under this operating condition, it can take into account the removal rate of pollutants, biofilm growth rate, and biofilm activity. It is the best starting condition and is expected to shorten the starting time by 23%.