If the start up hydrophobe of supercritical once thorough boiler is jetted into deaerator,the water and heat amount in the hydrophobe will be completely recycled.Due to sudden drop in pressure,the kinetic energy of hydrophobes may impact and damage the parts inside the deaerator and the noise level caused by steam jetted into water may reach nearly 100dBA.To solve the problem,a steam ejector and a micropore muffler were deigned for noise reduction and their effects were compared by experiments.The results show that by the steam ejector the noise level can be reduced to below 80dBA,due to that the steam is cooled and condensed by supercooled water in the steam ejector.The micropore muffler can not cool the steam before it is jetted into the deaerator,so the minimum noise level is more than 80dBA.By this token,the effect of steam ejector is better than that of micropore muffler in reducing the noise caused by steam jetted into water.