Augmentation index (AIx) calculated from the pressure waveform of an artery is widely used to quantify the arterial stiffness and evaluate the cardiovascular risk. The key for calculating AIx is to locate the inflection point on the waveform signal, which is caused by the wave reflection. This study applies the probability distribution of the pressure waveform to identify the inflection point for estimating AIx. The results show that the pulse wave probability analysis not only can estimate AIx with a better tolerance of noise interference, but also allows for simultaneously monitoring, locating and characterizing other physiologically significant points on the pressure waveform.