The method of underwater deep cement mixing is a newly adopted and increasingly developed technique of underwater foundation treatment in China.Based on the marine projects being or to be constructed in Guangdong-Hong Kong-Macau Greater Bay,design characteristics of underwater composite ground with deep cement mixing,as well as the corresponding superstructures,were surveyed and analyzed.On that basis,systematic analysis was carried out on the potential testing methods corresponding to drilling core,vibration sampling,wet grab sampling,cone penetration test,borehole radial loading test and plate loading test.Finally,combined with engineering practice,comprehensive comparison was made with the above test methods,and suitable testing methods to be adopted were recommended for underwater composite ground with permanent DCM clusters and trial DCM clusters.