In order to study the occurrence mechanism of advanced coal pillar instability failure and support crushing accidents during a long-wall face passing across abandoned roadways period, the Panel LW3101 in Shenghua Colliery was taken as a typical engineering background. By means of in situ investigation, physical simulation experiment, theoretical analysis, in situ tests, and relevant monitoring methods, the occurrence mechanism and prevention measures are studied. The results show that the bearing stress in advanced coal pillar is accumulated larger and larger with the width of advanced coal pillar gradually decreasing, and meanwhile, the key stratum in overlying strata would also be sliding instability under some minimum critical width condition; the sudden failure of advanced coal pillar which leads to a sharp increase of bending moment is the key factor that induces fracture of the main roof in front of long-wall face, and the advanced fracture of the main roof can be prevented by changing the stress state of the advanced coal pillar from a two-dimensional state to a three-dimensional state; the method of backfilling abandoned roadway is used to improve the stability of advanced coal pillar and the corresponding monitoring results verify that this method is effective. The research conclusions provide a theoretical foundation and new guidance for preventing advanced coal pillar instability failure and support crushing accidents under a long-wall face passing across abandoned roadways condition.