Wave intensity analysis is a time method for studying waves in elastic tubes. Usually, the forward wave intensity is positive and backward wave intensity is always negative. The reflection coefficient RWI, which is defined as the magnitude ratio of reflected wave intensity and incident wave intensity, can be used to estimate the blocked extent. In this paper, we set up experiments in which we generated a single semi-sinusoidal wave in long elastic tubes and measured pressure and velocity at the middle sites of the tubes. When the tube is 100% opened, 25% blocked, 50% blocked, 75% blocked and 100% blocked, we obtained five different reflection coefficients RWI respectively. We concluded that wave intensity analysis provided a convenient, time based technique for estimating the blocked extent by analysing the reflection coefficients RWI of a tube. This conclusion is helpful for study waves of blood flow in arteries.