Abstract: Since the GJB 150.3A “Military Materiels Laboratory Environmental Test Methods: (Part 3) High Temperature Test” was enacted in 2009, in the applications of its high temperature diurnal cycle storage and operation, the constant temperature storage and operation test procedures, many questions remain to be cleared. This paper (in two parts) makes a detailed analysis of the simulated environment of these procedures, the application object and its characteristics. The first part is focused on the test procedures and their relationships with GJB 150.3 and MIL-STD-810C. The second part discusses the application object types of the storage and operation test procedure conditions based on the natural and induced temperature diurnal cycle data in GJB 150.3A. Some other questions, misunderstandings and problems in the engineering applications are also discussed in the second part. The following text is the first part.