In this paper, we deduced theoretically the relation between ion current and multiphoton dynamic parameters in (3+1)RMP1 process and presented a method for obtaining three-photon absorption cross section, four-photon ionization cross section and radiationless relaxation rate by RMPI technique. The dynamic parameters of Rydberg states of toluene in gas phase are experimentaly measured for the first time. The results agree with the typical expected range of magnitudes.