Rockburst is often encountered in the underground engineerings of high geostress area, it is a kind of dynamic geodisaster.Depending on the examples of rockburst in the Erlang mountain highway tunnel and Jinping second powerstation tunnel, the fracture geometry shapes of rockburst are elaborated. Through the research of SEM analysis and rock mechanics tests of rockburst, three basic mechanics mechanisms of rockburst have been summarized,i.e., compression cracking, compression shear cracking,bending and breaking.