在超声检测中，被检工件表面粗糙度不同导致耦合损耗不同，往往使探伤灵敏度降低。目前常用的补偿耦合损耗的方法是根据材质制作对比试块，但该方法费时费力。根据大平底回波声压公式推导出了工件表面粗糙度和补偿量之间的关系，可直接通过计算得到表面粗糙度引起的衰减量。制作了具有不同表面粗糙度的对比试块，通过试验验证了推导公式的正确性。

In ultrasonic testing, the variation of surface roughness of workpiece tested induces various coupling losses, as a result the testing error is inevitable. The common method to compensate the coupling loss is to make various reference blocks according to the material of workpieces, obviously it consumes time and labor. An universal equation, which can be directly used to compute the compensation resulted by the surface roughness, was deduced according to the flat-bottomed echo formula. Reference blocks with various surface roughness were made and used to verify the validity of the equation deduced, and the experimental results proved its correctness.