Under the same testing condition,circular friction blocks with three different sizes of train disc brakes were used to carry out comparative experimental study of frictional noise on brake dynamometer.Equivalent sound pressure level analysis and frequency domain analysis of these noise signals were performed,to study the influence of friction block size on brake noise characteristics.The interface morphology was analyzed by using optical microscope and twodimensional profiler after the experiment,and the length of friction arc on the friction interface was calculated,to reveal the influence mechanism of friction block size on brake noise behavior.The results show that,under a certain test condition and when the total apparent contact areas are made to be identical,the large circular block can effectively contain the brake noise,while frictional noise generated by two intermediate circular blocks or three small circular blocks exhibit high intensity.Compared with large circular block,on the surface of intermediate and small circular blocks there exist irregular wear features such as obvious ploughing and detachment,these characteristics lead to high intensity brake noise.The frictional arcs of large circular block are much shorter than those of intermediate and small circular blocks,this is also an important factor causing the reduction of brake noise intensity of large circular block.