Abstract: The existence of short-circuit current in the inner layers of poly-crystalline photoelectrochemical electrodes was postulated.Principle and experimental method for the measurement of such current ("dark current") were laid out and tested with simulated electrode system and actual polycrystalline photoelectrochemical electrodes.It was found that both open-circuit voltage and output characteristics of photoelectrodes are affected by dark current,whose magnitude depends heavily on the method of electrode fabrication.So it seems proper to suggest that polycrystalline photoelectrochemical electrodes should be made as compact as possible.