Abstract: The blowoff impulse of three different materials irradiated by soft Xray was studied on QiangguangI pulsed accelerator. The experimental results show that the coupling coefficients of blowoff impulse for grey paint, white paint and aluminum alloy irradiaded by Xray, the enegy of which was in the range from 0.20keV to 0.33keV and the average pulse width of which was 39ns, were in the range from 0.61Pa.s/(J·cm-2) to 0.80 Pa·s/(J·cm-2), from 0.58 Pa·s/(J·cm-2) to 0.97 Pa·s/(J·cm-2) and from 0.61 Pa·s/(J·cm-2) to 0.84 Pa·s/(J·cm-2), respectively, when Xray energy flux was in the range from 92J/cm2 to 136J/cm2, from 115J/cm2 to 159J/cm2 and from 163J/cm2 to 192J/cm2, respeclively.