The purpose of this study is to develop a computer simulation program for analyzing load transmission and vibration, characteristics of a helical gear system in the design stage.In this analyse, the transmission error, load distribution, root stress, contact area, and vibration characteritics are investigated. That is, the influence function of deflection is obtained by finite element analysis and the influence function of approach and gear tooth error are considered. Load distribution, transmission error, and contact area are calculated by solving load-deflection equation which includes these influence functions and tooth error, and the influence function of the bending moment is obtained by finite element analysis. The root stress is calculated by the load distribution and the influence function of the bending moment.Also, mass/damping/non-linear spring model for the gears is used and the vibration levels due to tooth error are calculated. The results of the simulation are cross-checked through a specially designed experimental set-up.