The symmetrization of the magnetic trap allows to reduce the transversal losses and to increase the equilibrium β at preservation the axial asymmetry. The symmetrization principles are obtained using the topography of the module of a magnetic field B. Two principles are formulated: “Natural” Principle and “Isometric” Principle. “Natural” Principle: the isomagnetic lines (isolines B on the equilibrium magnetic surface Ψ) do not form the islands, i.e. all isomagnetic lines are closed around the magnetic axis (for closed systems around the torus as in tokamak). “Isometric” Principle: at fulfilment the “Natural” Principle the equality of the field lines lengths between any isomagnetic lines on an equilibrium surface Ψ is necessary. The known omnigenous, quasi-symmetric and orthogonal magnetic traps satisfy to this last principle.