Poisson's ratio contains rich geological information, the degree of basic lithology of crustal rock can be identified from the Poisson's ratio, and thus it could be used to analyze geodynamics and metallogenic background. The seismic phase data of local natural earthquakes ranging from the 1980s to the end of 2017 were collected from the data sharing platform such as China Earthquake Data Center in this study. Furthermore, 11410 earthquakes (M ≥ 2.0) in South China were obtained through screening procedure. According to the linear equations of travel time-epicenter distance relation fitted by least square method, the average velocity of Pg-wave, Sg-wave, Pn-wave and Sn-wave were 6.11 km/s, 3.60 km/s, 8.06 km/s, and 4.59 km/s, respectively. The average velocity ratio (Vp/Vs) of the crust of South China was calculated to be 1.697 and its Poisson's ratio was 0.234; In addition, the calculated average velocity ratio near the crust-mantle boundary of South China was 1.756 and its Poisson's ratio was 0.260. The results of Poisson's ratio using the travel-time tomography method show the petrologic differences among the Yangtze block, Cathaysia Block, and Southeastern coast crust. The large low Poisson's ratio area between the Yangtze block and Cathaysia Block is well correlated with the Jiangnan orogeny belt, and the relatively high Poisson's ratio correlated with Qinhang metallogenic belt and Southeast coast are interpreted as underplating of the mantle derived magma.