Abstract The microtremor array method is used to detect underground Karst in Jiangxia district, Wuhan metro line 27. Based on the spatial autocorrelation theory(SPAC), the Rayleigh wave velocity dispersion curves are extracted, and through the inversion of dispersion curves,acquires the S-wave velocity structure and 2D profile. The results show that the research area top-down can be divided into four layers. The low-speed areas are developed in the third layer, suggesting that low-speed areas would be karst structures and are not small scale. Compared with the engineering drilling chart data, the stratigraphic stratification and Karst scale results of the SPAC method are basically consistent with the actual result.