The online measurement for slurry pH value has not been realized in concentration plant at present.In order to solve the problem of slurry pH value online measurement, this paper introduces several current methods for slurry pH value such as pH test paper, glass pH electrode and acid alkali titration, and summarizes their technical principle and existing problems.Basing on the studying on relationship between solution pH value and absorbance in phenolphthalein indicator pH value change interval, builds a brand new phenolphthalein photometric pH value measurement method basing on the regression analysis.Studies the photometric detection device and on-line sampling device core components, and develops successful the slurry pH value online measurement.The technology and instrument developed in this paper have been tested and applied in concentration plant, and the industrial experiment shows the technology and analyzer have high measurement accuracy, stable and reliable operation, really solve the online measurement problem of neutral slurry pH value, and have a good popularization prospect.