The dry adiabatic lapse rate of atmosphere should be referred to ‘vertical temperature lapse rate of dry air whose vertical motion characteristics is neutral’. There are two errors in the derivation of dry adiabatic lapse rate(γd) in existing textbooks: 1. The work done by gravity field is not considered; 2. Only the volume work exchange between air parcel and surrounding atmosphere is considered, and the heat exchange between them is arbitrarily ignored. When the size of air parcel is reduced from meters to nearly nanometers, the specific surface area will increase dramatically, and the corresponding heat transfer rate will also increase dramatically, so it is inappropriate to ignore all the heat exchange of any size air parcel in vertical motion. It is the overall microstructural characteristics of atmosphere that determine the stability of atmosphere, not the motion characteristics of an air parcel with a specific size in a specific movement. Hypothetical simulation from the perspective of random micro-perturbations of atmosphere is the most concise and powerful way to derive γd. Combined with the process of proving the stability of atmospheres with different vertical temperature distributions, the true meaning of γd and the method of derivation can be more fully explained.