The invention provides a method for determining deep covering layer lower slope bed rock surface impervious wall drilling. A bed covering interface is determined mainly according to effective combination of a percussion drill and a pilot hole; and according to the form of the bed covering interface, a foundation surface is determined by using a flat beating method. The method can reduce the construction footage of a pilot hole covering layer, guarantees smooth actuation of subsequent construction, solves the problem of high authentication difficulty of deep covering layer slope section bed rocks, and reduces the construction difficulty of a slope bed covering interface.