Organic light-emitting diodes (OLEDs) with the structure of indium-tin-oxide (ITO)/NPB/inserting layer/Alq/LiF/Al have been fabricated. The electroluminescence (EL) spectra of devices with different driving voltage and the characteristics of voltage-current-luminance have been measured. It has been observed that an irreversible process on the EL performance, such as luminescence spectra, bright, efficiency, begin to occur instantly if the voltage increase to some value. The related mechanism has been analyzed. The nanometer-thick inserting layer near the recombination zone may lead to local accumulation of carriers or charges, and result in a local breakage or phase transition of the inserting thin layer. This study shows that a nanometer-thick organic layer should not be used in OLED for preventing this invalidation process.