Abstract: The paper reports the experimental study of back-streaming ion effect in the target region of Dragon-I linear induction accelerator(LIA). The double-foil technique was used in the experiments. A thin target foil was used to generate backstreaming ions via interaction with electron beam, and a set of beam profile measurement system based on optical transition radiation (OTR) was used to record the time-resolved beam profiles. The study has proved the existence of backstreaming ions in the target region of Dragon-I LIA. The influences of backstreaming ions on high-current relativistic electron beam were observed by using different foils. The beam will partially focus and partially defocus with a metallic foil (Mo), while dramatic transverse motion will occur with a polymer foil (Kapton).