Abstract: The desiccation cracking of soils is a widespread natural phenomenon, the existence of which greatly deteriorates the engineering properties of soils. There is a lack of engineering materials on coral islands. How to use the locally sourced coral silt, a potential engineering material, and improve its engineering performance is a key problem that needs to be solved urgently. The PVA fiber is used to improve the desiccation cracking characteristics of the coral silt. Through the desiccation cracking tests and the image processing technology, the changing laws of crack parameters, fractal dimension, frequency distribution and propagation velocity of the coral silt are obtained. Thus, the dynamic evolution laws of desiccation cracking of the coral silt and the fiber reinforcement effects under different fiber content are obtained. The results show that the incorporation of PVA fibers improves the overall performance of the coral silt and acts as a bridge, which can hinder the shrinkage of the soils and inhibit the expansion of desiccation cracks to a certain extent. The cracking criterion of fiber-reinforced soil is obtained, moreover, the fiber reinforcement mechanism of the coral silt is revealed, which is of great significance to the potential application value of the coral silt.