In this work, the K-Na and Ca-Mg based raw materials were used to prepare SiO2-Al2O3-K2O(Na2O)(K2O-Na2O) and SiO2-Al2O3-CaO-MgO(CaO-MgO) system ceramics, respectively. The impacts of flux systems (CaO-MgO, K2O-Na2O) on sintering characteristic and mechanical properties of ceramic slabs prepared at different firing temperatures (1 110～1 210 ℃) were investigated systematically, and the evolution rule of phase composition and microstructure was studied by XRD and SEM. The results show that the optimal firing temperatures for CaO-MgO and K2O-Na2O system ceramics are 1 170 and 1 150 ℃, respectively. The introduction of Ca-Mg based raw materials would lead to the lower firing shrinkage and bulk density of CaO-MgO system ceramics compared to K2O-Na2O system ceramics, meanwhile the pore size and content in CaO-MgO system ceramics are larger than those in K2O-Na2O system. The formation of anorthite and α-cordierite in CaO-MgO system ceramics is promoted by the introduction of Ca-Mg based raw materials, and the crystalline phase content of CaO-MgO system ceramics is significantly increased to be 75.66%(mass fraction), which is 56% higher than that of K2O-Na2O system. The dispersion strengthening effect caused by high crystalline phase content is greater than degradation effect of pore on mechanical strength. The flexural strength of CaO-MgO system ceramics is (56.9±2.6) MPa, fracture energy is (183.2±9.5) J/m2, failure strain is (7.4±0.1)×10-4 and specific strength is (24.9±1.1) kN·m·kg-1, which are 15%, 25%, 11%, and 23% higher than those of K2O-Na2O system ceramics, respectively, indicating that the CaO-MgO flux system is more suitable for the manufacturing of high strength, toughness, and flexibility ceramic slabs compared with the traditional K2O-Na2O system.