In this paper, an ultra-fine-grained Mg-2.5Zn-1Ca alloy was prepared by extrusion + equal channel angular extrusion (ECAP) composite processing technology. The microstructure evolution characteristics during the deformation process were analyzed by OM, SEM, XRD, EBSD etc., combined with mechanics performance changes, study alloy strengthening mechanism during deformation. The results show that after extrusion + ECAP deformation, the grains and the second phase grains are significantly refined, and the uniform fine grain structure is obtained after extrusion + 2 passes ECAP, with an average grain size of about 1.1μm; At the same time, the fine Ca₂Mg₆Zn₃ particles are dispersed distributed in the matrix. The grain refinement is the result of the combined effect of severe plastic deformation, dynamic recrystallization, and the finely dispersed Ca₂Mg₆Zn₃ phases. ECAP deformation significantly improves the mechanical properties of the alloy. The two passes have the highest tensile strength and elongation, which are 275MPa and 17% respectively. With the increase of ECAP deformation passes, the texture strength gradually weakens, and the basal texture gradually changes into a new texture. Moreover, ECAP deformation alloy has higher non-basal Schmid factor, and the microstructure is uniformly refined, which makes the material have better elongation.