Mg alloy has hexagonal structure and exhibits poor workability at room temperature, which is attributed to the difficulty in activating a sufficient number of independent slips to accommodate the deformation. Twinning plays an important role in plastic deformation of Mg alloys during low and medium temperature to accommodate the imposed strain, especially the strain along the c-axis. Therefore, the microstructure and texture evolutions of AZ31 Mg alloy during multi-pass compressions at room temperature were investigated by EBSD technology. The results show that the microstructure and texture evolutions are mainly controlled by tension twinning during multi-pass compression. And the more the strain passes, the severer the texture transformation. The c-axes of the grains are almost rotated to the compression direction by tension twins. The twins generated during multi-directional compression can separate grains and then refine them. However, the de-twinning can rotate the grains back to the initial orientations, which is against the texture weakening. The Schmid law governs the characteristics of {10\bar{1}2} twinning, and thus controls the texture evolution. Both the residual matrix and the pre-deformation induced twins intersect with the twins generated during subsequent deformation. And this can separate the grains and weaken the texture strength. The number and morphology of the activated twin behavior during multi-pass compression would be influenced by the pass reductions, consequently affecting the grain refinement.