An operating method for a power train of a hybrid vehicle having an internal combustion engine, an electric drive machine and a rechargeable electric energy storage unit configured to supply the electric drive machine with energy, includes controlling the power train in a zero emission mode in which the internal combustion engine is deactivated and in which the electric drive machine serves to drive the hybrid vehicle, and in an emission mode in which the internal combustion engine is operated in a fired operation. The method also includes determining, for a system initiated change of operating mode from the zero emission mode into the emission mode, a starting command for the internal combustion engine. The change of operating mode from the zero emission mode into the emission mode is blocked for one of a predefinable delay time, a predefinable quantity of energy extracted from the electric energy storage unit, or a predefinable travel distance.