Abstract: In order to solve the problem of large deformation and serious failure in rock crosscut over which working face cross, the theoretical analysis method was used to study the critical safety rock pillar thickness and strengthening support distance of the roof in the fully mechanized mining face. The results show that the stability of crosscut decrease with decrease in its vertical distance with respect to working face, and vice versa. For a given geo-mining condition, there is a critical safety rock pillar thickness between working face and crosscut, which can be used to determinate the span of reinforced support. The critical safety rock pillar thickness of the roadway support consisted of failure depth of working face floor, thickness of bearing stratum, and failure height of crosscut roof, and their calculation formulas were obtained using limit equilibrium theory of rock masses, Winkler elastic foundation beam theory, and equilibrium arch theory, respectively. Based on the obtained critical thickness of safety rock stratum, span of reinforced support in rock crosscut could then be determined.The engineering application was carried out with the No.11002 mining face of Wantian coal mine as an example, it is calculated that the failure depth of working face floor, thickness of bearing stratum, and failure height of crosscut roof were 2.9 m, 3.4 m and 0.7m, respectively. Considering a certain safety coefficient, the thickness of safety rock stratum was determined to be 10.5 m, and the span for required reinforced support was 29 m, including 14 m backfilling support and 15 m timber-lifting support. The engineering practice shows that reinforced support could not only ensure the roadway stability, but also increase the recovery rate and produce considerable economic benefits.