A method that makes it possible to analyse a vehicle drive system with a compound parallel power flow transmission even as early as at the project design stage has been presented. The essence of this method lies in determining the values of two characteristic transmission speed ratios i1 and i2 of the compound system at which the power transmitted by the continuously variable transmission (CVT) changes its sign, referred to as “zero-power” speed ratios. These speed ratios determine the power curve in the whole speed ratio regulation range from i1 to i2 and thus, the speed and torque curves at the CVT input and output shafts. Thanks to this, the structure of the compound transmission can be so selected that the loads of individual CVT subassemblies would not exceed the acceptable levels and they would be kept within the predefined limits. As an example, the drive trains of four gearboxes with parallel power flow, possible to be found at present in Poland, were analysed with the use of this method, i.e. the Voith DIWA and Allison EV Drive models and a prototype built at the Lodz University of Technology (TUL), designed for city buses, and the Toyota Prius or Lexus passenger car gearboxes. Moreover, a CVT friction gear and a conventional gearbox were analysed for their properties to be compared with those of the parallel power flow systems.