Abstract: Immediate roof of B²₁₃ coal-seam is gravel seam bonded with gravel and sandstone in Shajihai Colliery which brings difficulty for roadway supporting.So it is necessary that researching gravel granularity and strength characteristic of boulder bed.Gravel quantity and volume percent was analyzed by statistics.Single-axial compression strength was tested by point load method.Results showed that single-axial compression strength of gravel was very large,especially that of lividity gravel usually was over 200MPa,even reaches over 300MPa.