Abstract: Earthen structures, one of the most earliest architectural style, are widely distributed all around the world. There are lots of earthen heritage sites that still remain in northwest of China. The variety of earthen structures ranges from simple forms to vast, and the construction techniques varies from culture to culture and region to region. However, the majority of historic buildings and archaeological sites made of earth exhibit serious conservation problems due to various environmental conditions. Among these styles of deteriorations, fissure is one of the most common and widely developed diseases on earthen sites, which has a great influence on structural stability of sites. According to the in-situ engineering data obtained in recent 5 years, from the ancient rammed-earth ruins in Gansu and Qinghai provinces, which can date back to Ming-Dynasties, this paper analyzes the influence of primary meteorological factors, i.e.rainfall, evaporation, temperature, daily temperature difference and sunshine, on the development of fissures in the rammed-earth sites. The results of this study well reveal the meteorological environment effects on the development of fissures. The analytical data shows that the fissures in the ancient rammed-earth ruins suffer different actions of the meteorological factors in the northwestern of China, such as rainfall, evaporation, temperature and sunshine etc. The main conclusions are as follows:(1) the average fissure length and maximum fissure length tend to increase with the increasing of rainfall, decreasing of evaporation, reducing of temperature and decreasing of sunshine; however, the fissures have a tendency to expand in humidity environment.(2) the average fissure width and maximum fissure width tend to increase with the decreasing of rainfall, increasing of evaporation, increasing of temperature and sunshine; meanwhile, the arid environment can have a positive effect on the development of tiny fissures in the early stage.(3) the impact of the meteorological environment on the sites is a complex process. The factors are various and have a mutual influence which promotes each other. As a result, the impacts of these meteorological factors on earthen sites are similar.