Abstract：The pseudo-triaxial compression tests and confining pressure reduction tests were carried out for coal specimen strengths in different stress on servo-controlled testing machine. Under the action of confining pressure，coal specimens with fissures closed can bear the weight through fissure friction. The deformation properties of coal specimens before peak stress are basically similar. Yield terraces in the peak of the stress-strain curve of coal specimens occurred in confining pressure reduction tests，and the post-peak plastic properties are more enhanced than that in pseudo-triaxial compression tests. Axial deformation value while coal specimens damaged are dominated by their pseudo-triaxial compression stress-strain curves. The strengths of coal specimen under pseudo-triaxial compression and confining pressure reduction tests are both linear liner relation with their confining pressure，and the confining pressure influence coefficients are basically the same. The internal fiction angle of coal specimens having no relation with loaded type can be used to represent mechanic property of material. The compression strengths of coal specimens in confining pressure reduction tests are lower than those in pseudo-triaxial compression tests at the same confining compression. The reason is that coal specimens have inner damage under the action of higher-axial compression.
