A method and an arrangement in power transmission of a forest machine (1), the forest machine including a primary power source (5) for generating power required for moving and controlling the forest machine and/or actuators (6, 7) therein. In the present method and arrangement, at least part of the power generated by the primary power source (5) is converted into electric energy by a generator arrangement (8). This electric energy can be stored at least partly in an electricity storage unit (9), from which part thereof can be used, when required, for generating pressure medium-transmitted power for implementing a pressure medium-transmitted function of the forest machine (1) or at least one actuator (6, 7) therein.
