The combination of the RF segment of the RNP procedure and the traditional ILS precision approach procedure can make full use of the advantages of the two types of procedures, but the transition phase of the two procedures needs to consider the design of the maximum descent angle. This paper analyzes the plane and section geometric design parameter limitations of the transition phase procedure, and analyzes the operating limitations of the transition from satellite-based navigation to ground-based radio navigation that require stable interception of heading signals and glide slope signals. Combining two types of limitations, this paper designs a method that can calculate the relationship between the deviation of the glide path and the arc distance to the final approach course fix point (FACF) from different final approach point (FAP) heights to determine the maximum descent angle. Through simulation verification, it is proved that the proposed method can calculate the maximum descent angle that meets the two types of limitations under the different transitional flight lengths and different final approach descent angles, and according to the given maximum program hypothetical temperature. This method provides a theoretical basis and feasible design method for the descending profile design of the transition between the RNP procedure and the ILS procedure, and can provide a reference for the actual design of this type of procedure.