Cascading channel estimation is the main challenge in implementing reconfigurable intelligent surface (RIS) assisted multi-input multi-out (MIMO) communication systems. With the increase of paths between the RIS and the base station (BS) (RIS- BS), more environmental interference factors are introduced, which makes the existing algorithms have defects in the stability of estimation performance. This paper presents a method named Multi-Path-Based Cascaded Channel Estimation Procedure (MP-CCE). Based on the Two-Step (Subspace) Multi User Joint Channel Estimation Procedure (S-MJCE) algorithm, the practicality of the algorithm is enhanced by reasonably adding environmental factors between RIS-BS. The simulation results show that the complexity of the MP-CCE algorithm and the S-MJCE algorithm is on the same order of magnitude, where the former has slightly increased complexity, but its estimation performance stability is significantly better than the S-MJCE algorithm and the simultaneous orthogonal matching pursuit (SOMP) algorithm.