An N-channel VDMOS I-V curve is measured after X-ray radiation under condition of different power dissipation. It is found that the property of new interface traps induced by X-ray radiation of self-annealing VDMOS sample does not conform to existing theory reasonably well. Based on measured data，we advance the viewpoint that the interface trap has current conductive property besides being charged up, and the conduction is assumed to be the generation or recombination current caused by new interface traps, which can not be simply identified quantitatively from the I-V curve.