In 1964, Howard Gage reported on the harmonic ratio in accelerometer analysis of human gait. Although this index was used in gait analysis with a flat surface, it was necessary to examine the possibility of evaluating gait on stairs due to the hazardous areas of slips, trips, and falls. The aim was to develop a simple gait index for stair climbing up and down, and the application of harmonic ratio in stair movement was expected to indicate different values between up and down. It was well known that there was a significant difference between walking on a flat surface and stairs down, and this could be applied to the evaluation of indoor walking hazardous areas.