Abstract The helical gears are widely used in different engineering applications especially in case of vehicles on the gear boxes. The aim of this research is the analysis of the effect of number of teeth on the pinion beside of the constancy number of teeth on the driven gear. Five types of helical gears have to be designed for the comparative analysis. Own-designed designing software are necessary for the facilitation of the designing and modelling process. During this research the normal stresses and normal deformations will be analysed into different directions by TCA method. After the analysis the functions of the mechanical properties and the number of teeth will be determined.