For effective use of island reef coral mud, the performance of island reef coral mud was investigated to examine the cracking phenomenon when this coral mud was utilised as engineering material, and 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 used 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 patterns of coral mud cracking parameters such as crack development rate and the dynamic evolution patterns of cracks in coral mud after HPMC modification were investigated; Finally, the inhibitory effect of HPMC on the cracking behaviour of coral mud was analysed and the cracking inhibition mechanisms were described. The results of the study show that the addition of HPMC can significantly improve the anti-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. This can significantly optimise the overall performance of the coral mud surface layer and its anti-cracking performance.