The present invention provides a water quality monitoring data online processing method and device. The method comprises the steps of: obtaining a spectrum curve of water quality to be detected, setting a standard water quality spectrum curve as a reference, employing an autocorrelation function to calculate a related peak distance between the spectrum curve of water quality to be detected and thestandard water quality spectrum curve, and according to the related peak distance and sampling intervals, performing dynamic calibration of the spectrum curve of water quality to be detected; and performing noise removing processing of the spectrum curve after the dynamic calibration by employing a dual tree complex wavelet transform method, a threshold de-noising method and a dual tree complex wavelet inverse transform method, filtering the interference of noise signals, and finally, measuring a water quality reference value through a spectrometer according to the spectrum signals after noise removing process. Therefore, the spectrum signals with good repeatability can be obtained, the interference of water quality detection from outside environmental noise is avoided, and the accuracy of water quality detection is improved.