目前X射线机在无损检测领域发展迅速，但在测量物距时并没有考虑真实成像表面和成像板表面的距离，测量结果会存在一定误差，从而影响图像的不清晰度的计算。首先通过标准的阶梯试块测量出X射线机的最小分辨率。利用标准试块的试验结果，选择合适的电流电压等参数值对试块进行透射，然后根据理论公式计算出成像板表面和真实成像面的距离。试验对检测时得到更准确的物距，计算图像的不清晰度等有重要意义。

Nowadays, the X-ray machine is developing rapidly in nondestructive testing, but the distance between the plate surface and the real imaging surface was less taken into account. There are however, some errors in the measurement object distance, thus affecting the calculation of image unintelligibility. This article first measures the minimum resolution of X-ray machine through a standard step test block. Through the experimental results of the standard test block, the appropriate parameters such as electric current and voltage are selected to transmit some certain block. Then according to the theoretical formula the distance of the plate surface and the real imaging surface is calculated. So we can get more accurate object distance in the following nondestructive testing and have an important significance of calculating the unintelligibility of the image.