Al-Mg-Ti alloys containing La, Zr elements were prepared by cast metallurgy. Effects of La, Zr additions on microstructure and mechanical properties of Al-Mg-Ti alloy were investigated by property test, optical microscopy, scanning electron microscopy, energy spectrum and X-ray diffraction. The results show that the addition of 0.2%Zr can positively refine the grain size，which indicates the composite refining effect of Ti, Zr is compatible，and the brittle phases of Al3Zr precipitated in matrix can significantly increase the hardness of the alloys, but weaken the effect of grain refinement on the strength and ductility of the alloy. The combined addition of 0.2%La and 0.2%Zr possesses the most excellent grain refining effect, the average grain size of the alloy is dropped to only about 55μm and the addition of La can effectively avoid the precipitation and coarsening of brittle phase of Al3Zr, which makes the strength and ductility of the alloy improved significantly, and makes the hardness increased little.