Recently increasing number of gears for automatic transmission is main trend for development of automatic transmission, and its main target are a further significant reduction in fuel consumption and emissions, good driving performance. Surely increasing number of gears enables to reduce fuel consumption and good driving performances, because it also increases the number of available engine operating points, and enables engine to operate in more efficient states. In addition to these merits, increasing number of gears necessarily results in system loss, for example, a growth of cost and weight of automatic transmission and an increase of drag torque of friction components. To determine a reasonable number of gears, the fully consideration of these effects of increasing number of gears for automatic transmission is necessary. The analysis software for evaluating system performances was developed, and the analysis on the effects of fuel economy, acceleration performance, drag torque and hybridization was presented.