The relationship among each gear number of teeth for compound gear train with large transmission is studied

which includes a row of profile shift gear. Using method of CAD optimization design

the relationship among the characteristic parameter k for calculation of each gear optimum number of teeth

teeth difference x2=z2-z6

and x3=z2-z4 is determined. For selection of planner

the maximum transmission ratio and some larger transmission ratios of compound gear train are also provided.