敦煌莫高窟壁画长期受到外界微振动环境的影响，部分出现了裂隙病害，为此有必要深入开展壁画裂隙萌生特性的研究，为壁画的保护和修复工作提供科学依据和技术支持。针对莫高窟壁画地仗试件开展了四点弯曲抗拉试验，并利用数字图像相关技术实时测量了试件表面的全场应变变化与分布情况，分析了地仗在承受拉力破坏时裂隙萌生特性，给出了壁画所能承受的极限应变。同时，研究了试件缺陷、加载方式、疲劳次数等对试件的承载力与极限应变的影响。研究发现，莫高窟壁画裂隙萌生甚至一定程度的扩展并不会影响洞壁结构的承载力；壁画地仗的固有缺陷会导致壁画在缺陷处及其附近出现裂隙病害的风险加大；壁画地仗中添加的麻等纤维使其具有非常好的塑性和抗疲劳性能，只要在疲劳极限内就不会萌生裂隙。为了避免壁画产生裂隙病害，壁画地仗的最大正应变要严格控制在0.40%以内。

The wall-paintings of Mogao Grottoes have suffered from cracks initiated under the influence of external micro-vibration environment for a long time. Therefore, it is necessary to study the mechanism of crack initiation in the wall-paintings, which provides scientific basis and technical support for the wall-paintings protection and repair. Tensile strength is obtained by experiments of four-point bending on the plaster ground of the wall-paintings. Digital image correlation technique is used to measure the strain variation and distribution in real time. Besides, the crack initiation on the plaster ground is analyzed when tensile damage occurrs to obtain the strain limit of the wall-paintings. Moreover, the influences of initial flaw, loading method and fatigue cycle number on the bearing capacity and the strain limit of the specimen are studied. The results show that the initiation of cracks and even their development to some extent will not affect the bearing capacity of the grottoes wall structure. The initial flaw of the plaster ground can increase the risk of cracking around the flaw. Fibers such as hemp improve the plaster ground with better plasticity and durability, and reduce cracks within the fatigue limit. In order to avoid crack occurrence, maximum normal strain of the plaster ground should be strictly controlled less than 0.40%.