Abstract: This paper investigates coal strength and damage charateristics under bidirectional loading, obtains the mechanical parameters by testing the coal under uniaxial compression, then gets coal mesomechanical parameters through particle flow code(PFC) and fish program combined with the uniaxial experimental results. It conducts the research on coal strength, deformation and acoustic emission under biaxial loading. The main research results are reached as follows. In coal deformation and failure process under bidirectional loading, intermediate principal stress has the most significant effect on the yield stage, but no effects on the post-peak softening stage, which is different from the effects confining compression on the post-peak softening stage under triaxial loading. This result shows that coal under biaxial loading basically does not have the features of brittle converting ductile in post-peak stage. Coal volumetric strain under biaxial loading shows the three stages of linear volumetric strain decrease, nonlinear expansion and linear expansion. Intermediate principal stress has the most significant effects on nonlinear expansion stage, but no effects on other two stages. In coal damage and failure process, acoustic emission linearly increases at elastic stage, but the growth rate is smaller, nonlinearly rapidly increases at yield stage. It has the fastest growing near peak, reaches the maximum intensity at post-peak initial stage. Then the acoustic emission intensity decreases sharply. Acoustic emission maximum intensity lags behind the peak stress. The lag effect of acoustic emission maximum intensity relatively weakens along with the increasing of intermediate principal stress. Acoustic emission maximum intensity duration becomes longer with the increase of intermediate principal stress.