An experiment is performed to investigate the effects of several key factors on the efficiency of ammonia desulphurization.The experimental results show that it is possible to improve the desulphurization efficiency by some ways，such as increasing the liquid-gas ratio and slurry pH value，lowering the flue gas temperature or its flow speed.Based on the two-film theory，a mathematical model for ammonia desulphurization in spray towers is established.With the analysis on the correlation between the mass transfer rate equation of SO2 and the spiral-type nozzle droplet diameter，this model is used to calculate the main factors affecting the desulphurization efficiency.The calculation results are consistent with experimental data.