Abstract: The revolution difference of the low and high pressure rotors is a parameter for acceptance tests of a twin-spool turbojet engine.It indicates the relation between the reduced revolution of the high pressure rotor and the reduced turbine inlet temperature and also shows the matching between the low and high pressure rotors.In order to determine the revolution difference for a twin-spool turbojet engine it is necessary to define a standard revolution difference line for this type of engine.This paper analysis considers various possible approaches for the revolution difference line computation and suggests how to define the standard revolution difference line in practice.