Abstract: An organic thin film electroluminescen device emitting different color with different driven voltage has been fabricated. The structure of the device is ITO/SA/PBD/Alq³/Al. SA is a styrylphenylamine derivative and its full name is N-（2-p-methoxylphenyl）-styryl-N-p-methoxylphenyl-benzeneamine. SA can emit blue light with peak at 470nm. Alq³ is a chelate of aluminum with three 8-hydroxylquinoline and emits green light at 520nm. PBD, an oxadizole derivative, is used between SA layer and Alq³ layer to confine the emission both from SA and Alq³. The variation of electroluminescent spectrum with the voltage applied to device has been investigated. It is found that the emission spectrum of the device is consist of two parts, one is blue emitted from SA, the orther is green emitted from Alq³. And the blue part increases with increase of the driven voltage. An energy band model is established from the data of work function of the electrodes and the HOMO levels and LUMO levels of the organic materials. The EL behavior of the device has been explained by the energy band model.