AbstractMining height of coal seams plays a major role in the failure of the key stratum as well as combinational key stratum. Based on analyzing the relevant parameters of combinational key stratum, applying numerical analysis, the influence of mining height on combinational key stratum fracture, which is also the influence on the main roof weighting step, is studied and the computational formula of the main roof first weighting step in shallow seams is revised. The first weighting step of the Da-liu-ta 1203 working face, derived from the calculation through the revised formula, is very close to the actual measurement. The consistency proves that the revised formula has certain adaptability in calculating combinational key stratum weighting step in the thick loose layers shallow seams.