Abstract: A method for determining density variation ratio(DVR) of strips in a case was established basing on X-ray attenuation, and the accuracy(correctness and precision) of the method was investigated.The results showed that:1) the fluctuation of X-ray intensity and strips density indications of the device was less than 1% in 24hours, which meets the requirements of strips density test;2) the precision range of strips density(S_{ρ, r}) determined by X-ray was from 0.012 kg/m³ to 0.301 kg/m³, and its relationship with strips density was ln(S_{ρ, r})=-6.31+2.15ln(ρ);3) the absolute value of relative error was less than 5% when strips density in the case was over 200 kg/m³, and it would decrease with the increase of strips density;the precision of DVR(S_{DVR, r}) was 0.0141%-0.0719% and independent of DVR;4) comparing with the method of sampling from 9 points, the density determined by X-ray device was higher, and the value of DVR was lower and more accurate.