Rockburst disaster caused by coal pillar poses a serious threat to safety production in advanced mining technology, such as the technology of gob-side entry driving, which is employed to develop the mining rate of coal. In order to reveal the rockburst mechanism of coal pillar in mines from the view of energy evolution, the bursting liability of coal specimen is tested in a mine, where a rockburst of coal pillar happens in the third cycle of 6 # roadway excavation. The rockburst mechanism of the coal pillar is analyzed theoretically and simulated by FLAC. On this basis, an evaluation standard of energy density is proposed and realized for risk assessment of rockburst. Then, numerical models with two types are established, and the trend characteristics of energy density factor and vertical stress in two scheme types are studied. Based on research results obtained, the weak impact tendency of coal specimen and the moderate impact danger level of mining face are internal causes for rockburst disaster in roadway backfilling mining; meanwhile, the maximum value 51,351 J/m4 of energy density factor in coal pillar of 6 # roadway in un-backfilling mining scheme is 3.33 times that of 15,403 J/m4 in backfilling mining scheme, and the rockburst disaster happens in the 6 # roadway excavation when elastic deformation energy reserved in coal pillar is released suddenly. The research results could provide a theoretical reference for the prevention and control of the rockburst disaster in mining engineering.