Abstract: The RFPA2D numerical simulation software developed based on the microscopic damage mechanics was applied to analyze the stress distribution featur es of the Brailian spltting samples.The PC controlled test machine was applied to the Brailian splitting test of lump coal and the acoustic emission features of the coa I during the Brazilian spltting process was studied.The study results showed that the acoustic emission incident occurred during the whole lump coal spltting process W ould have different emission features at different loading stages.With the loading increased, the coal stress field would be changed time to time from the loading initial p eriod to the failure time and then after the failure, the tensile stress in X axial direction would have a "non-obvious-best obvious-less obvious" procedure.When the lump coal was going to be failed, the tensile stress would reach the peak value which could confirm that the lump coal spltting was a tensile failure.The acoustic emission inc ident occurred this moment would be the best obvious.