In order to achieve the effective use of island reef coral mud, the performance of island reef coral mud was investigated, and it was found that there was a cracking phenomenon when the island reef coral mud was utilised as an engineering material, so it is of practical significance to carry out the research on the cracking and modification of coral mud. Firstly, hydroxypropyl methyl cellulose (HPMC) and coral mud were introduced to prepare an indoor surface model for the cracking test. Images were captured at different time periods and then the changes in coral mud related parameters were obtained by image processing techniques; Secondly, the changing law of coral mud cracking parameters, crack development rate and other parameters and the dynamic evolution law of coral mud crack after HPMC modification were investigated; Finally, the inhibitory effect of HPMC on the cracking behaviour of coral mud was analysed and the cracking inhibition mechanism was described. The results of the study show that the addition of HPMC can significantly improve the cracking properties of coral mud soil samples, and HPMC can prevent the contraction of the soil body and inhibit the generation of cracks by reducing the content of free water in the soil samples and adsorbing the coral mud particles inside the soil samples to form agglomerates, which can significantly optimise the overall performance of the coral mud surface layer and the anti-cracking performance.