Abstract: High quality Doppler radar can always catch Narrow-Band Echo(short as NBE hereafter). Normally, NBE reflects the existence of boundary convergence line. Careful analysis on NBE can facilitate nowcasting of severe weather events and further understanding of their evolution. After detailed study on three cases concerning with NBE, it is concluded: (1) NBE triggered by fast moving echo in upstream is an important indication of disastrous wind;(2) NBE can develop into severe storm under proper conditions. There are often two stages during this kind of growing: the first is developing of initial echo, the second is snap growing of echo core;(3) Doppler radar reflects outflow of downburst as a nearly ringed NBE. Inside look on downburst can be obtained combining NBE with other data.