Reason analysis for nonuniform ammonia spraying in SCR system of domestic power plants at present was carried out.By optimization and regulation for ammonia-injection-grid(AIG)of the SCR systems in two power units

the maximum denitration efficiency which can ensure the qualified ammonia escaping value was obtained.The experimental results show that:after the AIG was optimized

with the denitration efficiency of 50%

the relative standard deviation of NOxconcentration at outlet of side A and side B of the reactor decreased from 31.59% and 40.44% to 9.25% and 8.97%

respectively;with the denitration efficiency of 74.3%

the relative standard deviation of NOxconcentration at outlet of side A and side B of the reactor can still reach9.89% and 10.75%.Experiment about the maximum denitration efficiency was performed after the catalyst was put into service for 16 000hours.The results show that

under 600MW load condition

the maximum denitration efficiency dropped from 87% to 75%

by about 12%.