Abstract: ‍ ‍In order to solve the problem of cascaded channel estimation in reconfigurable intelligent surface （RIS） assisted wireless communication system， an adaptive double structured orthogonal matching pursuit （ADS-OMP） algorithm based on compressed sensing （CS） is proposed in this paper.Existing dual-structured sparse orthogonal matching pursuit （DS-OMP） algorithm used the dual-structured sparseness of cascade channels， i.e.， row sparseness and column sparseness， to improve algorithm estimation performance， but required known channel sparseness information.Based on the existing DS-OMP algorithm， the ADS-OMP algorithm proposed in this paper designed reasonable judgment criteria and iteration thresholds to estimate the relative sparsity， so that the estimation of the cascade channel can be completed without knowing the row sparsity and column sparsity of the cascade channel in the angular domain. It effectively overcomes the dependence of the existing DS-OMP algorithm on the relative channel sparsity， which makes the proposed algorithm more practical. Simulation results show that the performance of the ADS-OMP algorithm proposed in this paper is consistent with that of the existing DS-OMP algorithm. Both algorithms are on the same order of the complexity， and the complexity of the ADS-OMP algorithm is slightly increased.