Abstract: This paper investigatesandproposes the breaking of cavity layered overlying strata effecting caving zone height, and provides the determination method and criterion of caving zone height of salt single well solution cavity by the key stratum theory. This paper establishes the determination model of key stratum of salt single well solution cavity layered overlying strata by the elastic thin circular plate theory, provides the determination method of key stratum of salt single well solution cavity layered overlying strata, establishes that the hanging dew diameter of ke y stratum of salt single well solution cavity layered overlying strata less than the 2a1 is the criterion of key stratum breaking, and provides the criterion for judging the key stratum producing hinge and does not collapse, or direct collapse when breaking, according to the mechanical relationship between the formation of key stratum fractured rocks.