根据金属材料平面应变断裂韧度的测试方法，选取紧凑拉伸试样进行合成标准不确定度评定，给出了不确定度的表达式及计算值。通过分析认为：条件载荷PQ对标准不确定度的影响最大，试样几何形状因子f(α)的影响次之；平均裂纹长度测量的准确性和精度是影响应力强度因子的主要因素之一。最后，分析讨论了试样加工、夹具设计、裂纹预制、裂纹测量对裂纹平直度和测量精度的影响。

According to the test method of plane strain fracture toughness for metal material, the compact tension specimens were adopted to evaluate the combined standard uncertainty, and the uncertainty equations and the calculated values were given. Through the analysis, it was considered that the standard uncertainty was most affected by the condition load PQ, and the specimen geometry factor f(α) had a minor effect on the standard uncertainty. The accuracy and precision of the measurement of average crack length were the main influencing factor of the stress intensity factor. Finally, the influence on the crack flatness and measuring precision was analyzed and discussed from the aspects of specimen machining, clamp design, crack prefabrication and crack measurement.