超声检测技术对缺陷的定位和定量检测有高准确性和高可靠性，其已在复合材料结构的检测领域得到十分广泛的应用。为了评定检测结果的质量，需要对复合材料结构超声检测的不确定度进行评定，以表征检测结果的可信度。基于超声反射法对碳纤维增强复合材料检测试块中不同尺寸的平底孔缺陷进行定量检测，采用底波幅值衰减6 dB的方法对缺陷边界进行标定，得到检出缺陷的尺寸，建立了不确定度传递的数学模型，分析了对检测结果产生影响的因素，包括试块、扫查方法、设备参数以及检测重复性等，给出了复合材料结构超声检测的不确定度评定结果。

Ultrasonic testing (UT) has been proven to be a high-accuracy and high-reliability Nondestructive testing (NDT) method for determining defect in composite structures, such as its size, location, depth etc. While enjoying widespread application, UT is now considered to be interpreted from the view point of uncertainty. This paper aims to evaluate the uncertainty in UT quantitative assessments for composites defect size. Ultrasonic pulse-echo method was performed on composite test block made of CFRP with flat-bottom holes of different diameters. The geometry of defect was determined by referring to bottom signal amplitude, which would attenuate by 6 dB. Various factors, including the test block, scanning method, instrument parameters, as well as the repeatability, have been taken into consideration. This paper also covers the methods and steps of the evaluation of uncertainty in defect determination by UT.