Using slag to prepare slag glass-ceramics is one of the main ways to improve the utilization rate of mineral resources. CaO-MgO-Al2O3-SiO2(CMAS) series pyroxene phase slag glass-ceramics were prepared using Bayan Obo tailings as raw materials by microwave one-step method. 835 ℃ was choosed as the crystallization temperature and the influence of microwave heating on the crystallization behavior and microstructure of glass-ceramics were studied. Effect of La2O3 addition on the crystallization behavior of slag glass-ceramics were discussed using La2O3 as the research variable. Compared with traditional heat treatment system, the microwave heating achieves higher crystallization effect in a shorter time. Here, the addition of La2O3 promotes grain refinement. According to the analysis of Raman spectroscopy, the addition of La ion will cause the increase of bridging oxygen in the glass network and increase the tightness and integrity of the crystal. The hardness is the highest when the addition of La is 4% (mass fraction), and the Vickers hardness reaches 829.22 MPa.