Abstract: Based on the distributive principle of X-ray’s energy deposition, a kind of analytical method for calculating the blow-off impulse induced by pulsed soft X-ray was presented, and experimental measurements of the blow-off impulse were carried out on “QIANG GUANG Ⅰ” accelerator. The results of this analytical method are in accord with those of BBAY formula and also agree well with experimental data. The analytical method is applicable to estimating the blow-off impulse induced by X-ray in engineering.