Earth-dwelling caves are a Chinese treasured historical cultural heritage. Nowadays, they are still widely used in some regions. They are primary ecological buildings with low energy consumption and nearly zero CO2 discharge, which is in accordance with the belief of sustained development and the requirement of low-carbon housing. The construction of these caves are mostly based on the local craftsmen’s experiences and there are no calculation and drawing designing, but they have been lived in for a hundred or even several hundred years without collapse, which is worth exploring the structural secret within them. This paper has studied the reasonable and scientific values of the present existing earth-dwelling caves from the perspective of structural reliability. According to the material and structural characters of these caves, the paper used a response surface method to calculate the structural reliability. The result showed that the index of structural reliability for the earth-dwelling caves was higher than that for the same structures set by the present code. This explored the scientific secret of the existence of these caves and the research achievement will also provide an effective method for the analysis of the structural reliability of earth-dwelling caves.