Abstract: Simulations of ultrasonic in the buffer rods using the finite element methods was presented firstly. It showed the reasons of the trailing signals and designed some kinds of buffer rods with different diameters by disturbing the cylinder/air boundary. Based on the data from the experiments, it was found that Aluminum buffer rods with a tapered shape and a double-tapered shape could well constrain the trailing signals. At the same time, the effect of the constraining became better and better with the rising of the angel of the double-tapered shape buffer rods in some ranges, thus leading to a high SNR.