[Objective] It is of great significance to identify structure of the critical zones (CZs) of the earth for better understanding the geochemical, ecological and hydrological processes occurring in the CZs. However, previous studies relied mainly on borehole drilling and profiles, which is far from enough to help draw a full picture of the underground structure of the CZs. To overcome this problem, in this study, attempts were made to combine borehole drilling with the seismic refraction tomography (SRT) method to test if the seismological method can effectively detect the structure of CZs of highly weathered regolith.[Method] To that end, case studies were carried out of the Sunjia Catchment of Yingtan and the terraces of slat bedrock along the Yangtze River in Changsha. The study areas are both located in the red soil region, but different in bedrock composition. The bedrock is red sandstone in the Sunjia Catchment and sedimentary slate in the terraces along the Yangtze River. Ten seismic lines were arranged in the two study areas, and each had a detection depth ranging between 25~30 m. In addition, a total of 13 boreholes were drilled in the two study areas. In the field investigation recognition capability and error range of the SRT method were evaluated.[Result] Results show:SRT can effectively discern propagation velocity of p-wave at different depths in the CZs, and determine depth of key interfaces. In Yingtan, the identified lower boundary of the Overburden layer varies in the range of 3.0~5.2 m, with root mean square error (RMSE) being 1.7 m, and the identified bedrock surface does in the range between 8.2 and 22.0 m, with RMSE being 7.0 m. In Changsha, the identified lower boundary of the first layer falls in the range of 8.1~13.2 m, with RMSE being 2.4 m, and the identified bedrock surface does between 18.8 and 22.9 m, with RMSE being 0.9 m. The prediction is in good agreement with the drilling observation. The seismic wave travels at 2400 m/s in red sandstone and at 2 000 m·s^-1 in sedimentary slate. Under flat terrain the overburden and bedrock are stable, while under sloping terrain, the overburden is thick on the top slope, and gets thinner on the mid slope. Landfills reduce the precision of seismograph in predicting underground structure for they have great impacts on the structure of the overburden layer, but not much on the structure of the deep underground. Groundwater in aquifers makes the overburden of the critical zones divided with the seismic refraction method tend to be thinner.[Conclusion] The longitudinal wave traveling through the subterranean layers of the CZs varies in velocity with the layer, which is the key to identification of the structural layers of the CZs by seismograph. SRT can not only improve the efficiency of field investigations, but also advance the development of the CZ three-dimensional mapping.