The boulders (spherical weathered granite) exist commonly in south China; and the compression strength of boulder can reach 100 MPa. The boulders occurred during shield tunneling of Fuzhou Metro Line No. 1, which would lead to potential safety risk. The microtremor method is adopted to detect the boulders of Fuzhou Metro Line No. 1. The application results are testified by borehole drilling. The working principle of microtremor detection method is introduced. The application results of the microtremor detection method to Fuzhou Metro Line No. 1 show that the abovementioned method is reliable and effective in complex urban area.