Here the biquaternionic model of electro-gravimagnetic field (EGM-field) has been considered, which describes the change of EGM-fields, charges and currents in their interaction. The invariance of these equations with respect to the group of Poincare-Lorentz transformations has been proved. The relativistic formulae of transformation for density of electric and gravity-magnetic charges and currents, active power and forces have been obtained.