Analysis of perspective flow diagrams of layered mining of high flat coal-seam in the Kuzbass Region is carried out. A conclusion in made on the necessity to consider the influence of the underworked massif of the 2nd layer in determination of the ultimate thickness of the interlayer coal pack. Analytical studies of the stress-and-strain state of the underworked massif have been made. Sizes of weakened coal zones are determined and recommendations are given how to determine the ultimate thickness of the protective pack.