The observation of the earthquake cluster from 1990 to 2015 in Hainan Island and its coastal areas was collected based on the idea of a "generalized repeat earthquake". This study investigates the wave velocity ratio (v_P/v_S) of the earthquake cluster zone to different stations around using the single station-single earthquake method and preliminarily analyzes the physical properties of the subsurface medium in the study area. The results showed that: (1) The average wave velocity ratio of the earthquake cluster to the single station was lower than 1.732. Before and after 2008, significant differences were found in the variation characteristics of the average velocity ratio and the velocity ratio with time, which may be related to the stress adjustment after the long-period seismic activity in the study area during 2007—2008 and to the stress transfer of the 2008 Wenchuan earthquake. (2) The v_P/v_S ratio was affected by the crushing degree and the rheological property of the subsurface medium. A high rupture degree of underground rocks and a strong rheological property of the medium may cause a relatively high velocity ratio of stations, such as the QXL, DOF, CHM, and NAD stations. (3) The underground medium in the uplift area of the central-southern Hainan was compact and stable. Aside from the NAD, CHM, and DOF stations in the special medium area, the wave velocity ratio of the other stations showed relatively low values in this area. (4) Before and after 2008, differences in the apparent velocity features and the seismic activities in different seismic cluster zones were found, which may indicate that the study area was in a state of stress adjustment. The different apparent velocities in the east and west sides of the Puqian—Qinglan fault were mainly affected by different lithologies and the thermal process in volcanic areas.