Abstract: Through-the-wall radar imaging by estimating the wall thickness and the dielectric constant is a hot research field in recent years. In order to lift strict restriction that the antenna should parallel to the wall in the traditional through-wall imaging model, and to solve the existing environmental parameters estimation algorithm with low computational efficiency and poor robustness problem, a novel linear MIMO array through-wall imaging model is proposed to adapt to the situation with unknown positional relationship between the array and the wall. Furthermore, based on the analysis of the echo path of the front and rear walls, this paper also presents a novel environmental parameters estimation algorithm with high estimation robustness and low computational complexity. Comparing to the conventional environmental parameters estimation algorithm, this proposed algorithm needs neither extra operations nor special targets to assist. The results calculated from Finite Difference Time Domain (FDTD) simulation verify the effectiveness of the proposed imaging model and environmental parameters estimation algorithm.