The value of the discoveries of Hamipterus tianshanensis and their 3D eggs fossils?are of?great importance.?These fossils preserved in Beijing for several years, the surrounding rocks have been powdering and flaking, which seriously endanger the safety to fossils. This paper intends to use XRF and other methods to detect surrounding rock to explore its corrosion mechanism. The analysis shows that the surrounding rock of fossils is composed of sandstone with boulder clay, which contains some clay minerals such as montmorillonite. The?sandstone?with?calcareous?and?salt?cementation contains large amounts of soluble ions such as Cl-, NO3-, Na+ and Mg2+. The mechanism of the deterioration is as followed, when the humidity changes, the soluble salt also generates large crystal pressure, as well as the expansion of clay minerals produces huge pressing force, leading the surrounding rocks to powder and flake gradually. The?solution?of?salt?existing?as the cement results in the escape and?migration of?particles, which?is?an important reason for fossil deterioration.?Based on the above understanding, this paper also gives suggestions about the protection of fossils.