Several dissipative solitons or soliton attractors have been investigated in dissipative nonlinear systems, but the quantitative theoretical frame for multisoliton attractors is still lacking, which hinders the quantitative investigation of soliton attractors. We provide a method to obtain a theoretical frame for multisoliton attractors in mode-locked fiber lasers with various initial states. These results provide possibilities for realizing controllable generation of soliton attractors. We further propose that the properties of soliton attractors can be used to calculate dissipation strengths. We perform experiments to observe the generation of multisoliton attractors in a mode-locked fiber laser and demonstrate the effectiveness of the calculation method for the dissipation strengths. Our results provide possibilities for studying the dynamics of localized waves quantitatively in nonlinear non-Hermitian systems.