Abstract: This paper includes two parts: the first part discusses the differences between environmental adaptability and reliability, environmental adaptability requirements and their characteristics, and methods for describing environmental adaptability. The engineering applications of “environmental adaptability” are also discussed. The second part first discusses the verification requirements of environmental adaptability, and the implications and deficiencies of the concepts of “environmental requirement”, “requirement of environmental technologies,” and “environmental conditions”, and proposes some more adequate definitions; then analyzes various types of environmental adaptability requirements and the related index system; finally demonstrates the index system framework of environmental adaptability requirement for the whole armament and its sublevel products with examples. Here is the first part.