Objective: To eliminate the noise of the plethysmography wave and obtain plethysmography wave signal without noise. Methods:Using sym4 and combining the improved wavelet threshold wavelet algorithm to remove high frequency white noise of plethysmography wave, and then using spline differential fitting method to remove baseline drift of pulse wave volume. Results:The experimental results show that the high frequency noise and baseline drift of plethysmography wave have been removed effectively processed by the sym4 wavelet and combining with improved threshold of wavelet algorithm and spline difference after fitting. Conclusion:The method can well remove the noise of the plethysmography wave and retains the effective information of plethysmography wave effectively.