At present

relatively few drilling surveys have been conducted on coral reefs

and comprehensive geological info on coral reefs is difficult to obtain. However

research on coral reef is of great importance to our development and exploitation of maritime resources. The survey of Chenhang Island in Paracel (Xisha) Islands saw China’s first usage of digital borehole camera technology

which resulted in a large amount of first-hand geological data

but the traditional rock mass integrity index (RMDI) method is not suitable for coral reef rock mass. To evaluate the size effect of cavities on coral reef rock mass

we proposed the concept of coral reef cavity density

and established the coral reef cavity density and block functions. Afterwards

the value of coefficient ? in the RMDI can be determined; the integrity index density function (DIDF) can be reconstructed; and then ultimately the coral reef RMDI can be determined and used to evaluate the coral reef rock mass integrity. The evaluation method is applied to the borehole CK1 of Chenhang Island in Paracel Islands. The evaluation results are generally consistent with other evaluation methods. Some conclusions are drawn as follows. High-resolution borehole images can provide reliable results for evaluation of coral reef rock mass integrity. The cavity density function can reflect the distribution of cavity effects on coral reef rock mass along the axial direction; DIDF is a good representation of coral reef rock mass integrity along the axial direction; The RMDI method is a feasible approach for the evaluation of coral reef rock mass integrity along the full or partial depth of a borehole.