The EIS type Light Addressable Potentiometric Sensor (LAPS) system is described. On the basis of experimental data, Authors analyze such parameters as bias voltage, light modulation frequency, light radiation power, which have great relationship with the EIS type LAPS′ photovoltage. Consequently, the optimized result of these parameters is given. A super Nernst function phenomenon in the relationship of photovoltage and pH value is reported.