Abstract: A test study on deep peak regulation at 30% rated load is carried out in a 330 MW circulating fluidized bed unit,the preparation work and matters needing attention in the course of deep peak-regulating diagnostic test are described in detail,and the test operation process,problems encountered in the process and adjustment strategies are introduced.The test results show that,the target of the original NO_x generation value below 50 mg/m~3 in DG1177/17.4-Ⅱ2 circulating fluidized bed boiler can be achieved under the 30%rated load condition by adjusting the air distribution,bed temperature and bed pressure.To prevent the adjustment of steam pressure,steam temperature and NOx emission value from disorder,the large addition and subtraction of coal should be avoided under low load conditions.The steam turbine adopts the single valve mode,which can effectively increase the reheat steam temperature.The results of this paper can provide certain reference for the deep peak regulation at 30% rated load of the same type of circulating fluidized bed boiler.