Fengguo Temple is located in the northeast of Yixian County, Jinzhou City, Liaoning Province. According to an inscription inside the temple, construction of the temple began in 1 020 AD, the ninth year of Kaitai during the Liao Dynasty. The main hall, Daxiong Hall, is so far the largest single wooden structure of all Liao Buddhist architecture. Daxiong Hall has a total of 20 mural paintings of the Yuan Dynasty with a total area of 466.7 square meters. These paintings are outstanding representatives of the fresco art of the Yuan Dynasty and boast high historical and artistic value. Due to an old age, several repairs and an unstable conservation environment, diseases, especially crack disease, have been very prominent, not only affecting the integrity and beauty of the mural paintings, but also destroying their safety and stability. For these reasons we selected the mural paintings of Fengguo Temple of the Yuan Dynasty as research objects. First of all, we determined the distribution of cracks, judged their types and summarized their characteristics. Then we evaluated the causes of cracks of the mural paintings with reference to the methods of analysis used for studying the causes of building wall cracks. Finally, we systematically and comprehensively summarized the cause of crack disease in the mural paintings in terms of crack attributes, causes and processes. From this study, it is shown that the building and foundation structures are stable that there is no uneven settlement. Cracks in the murals are due to temperature changes. The deformation stress caused by curing shrinkage and temperature shrinkage of epoxy resin is restrained in brick walls, which will be released in the earthen layer. This stress will cause deformation of the earthen layer and if the residual stress is still greater than the ultimate strength of the earth layer, the cracks will be earth layer.  In this study, we developed a new research system suitable for crack diseases of mural paintings by a combination of practical investigation and the analysis of influencing factors. This research system can not only provide a theoretical basis for the further protection of murals, but also, to a certain extent, make up for the gap in this field, making the disease analysis process of murals more scientific and logical. It also provides a reference for the analysis of crack disease in other areas.