The function of fast-cut back （FCB） is very important to maintain the stable of power grid and large thermal power plant. In the FCB test of 660 MW ultra-supercritical units in BuLian Power Plant, the normal combustion of boiler and the good furnace pressure could been maintained very well through the reasonable adjustment of coal mill trip order and intervals, as well as the coordination control of primary air, secondary air and induced air. The control method of HP and LP bypass, steam temperature and pressure, water level of condenser and deaerator were also discussed. The results show that the main parameters are fluctuated slightly and can be quickly stabilized. The rationality of control strategy and the integrity of logic function design are verified, which can provide references for the FCB test of ultra-supercritical units.