The effect of different bias voltages on microstructure of Al coatings on uranium was investigated by using scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray stress analyzer, respectively. The results indicate that the microstructure is influenced strongly by bias voltage. At low bias voltages, especially at -100 V, the structure of Al coatings is more densely packed than that at high bias voltages of - 300 V and - 400 V,where the structure looks like open dentritic. On the whole, the peak (111) orientation is predominant with the increase of bias voltage, but at -400 V, the diffractive intensity of main peaks (111) and (200) is close to the standard reference. The residual stress on Al coatings surface is small, which has a change from tensile to compressive stress with the increase of bias voltage.