The noise characteristics of light-addressable potentiometric sensor ( LAPS) are researched in this paper.By means of analyzing the semiconductor field effect device struc ture of LAPS, the theoretical model of LAPS sensor is constructed,and then the origin of noi ses,the type of the noises,and the noise characteristics of LAPS device are further analyzed .The concentration of hydrogen ion in pH buffer solution is chosen as detection targ et,and the LAPS measurement system based on NI data acquisition card and Labview -based environment is constructed in experiment.The experimental researches are made on the influence factors of the LAPS noise characteristics,including the wavelength,the modulation frequency,and the intensity of light source,and the thickness of s ilicon substrate. Results of the researches indicate that increasing the wavelength of light sourc e and enhancing the intensity of light source are the two most effective approac hes for improvin g the amplitude and the signal to noise ratio (SNR) of o utput signal.