This paper discusses the preprocessing procedures before power spectrum analysis of pulse transit time(PTT) variability,including the uniform resampling and removing the non-stationary trend.A resampling method using the average heartbeat frequency as resampling rate and a wavelet detrend method based on frequency control(WFC) are proposed.By analyzing the PTT sequence,we obtain the following results:1) using the average heartbeat frequency as resampling rate can both reach the goal of uniform sampling and ...