Abstract: Based on the photoswitchable characteristic of spirooxazines controlled by photochromic reactions,spiro2H-indole-2,3'- phenanthr oxazine（SO） as guest was doped to the active host MEH-PPV and the four layers architecture light-emitting diodes（LEDs） was fabricated using ITO as anode,PEDOT:PSS as hole-transport layer,MEH-PPV: SO as emitting layer,LiF and Al as cathode.The electroluminescent properties of LEDs was investigated by exposure to UV and visible light respectively.Through photochromic reaction,the ring-opening coloured of SO acted as traps for injected charge carries which influenced the behavior of LEDs.The electroluminescent characteristics of MEH-PPV diodes including current density,brighting and electroluminescent intensity may be changed through the reversible switchable charge traps of SO driven by light.