The effects of Gd content on the microstructure, mechanical properties and corrosion resistance of as-cast Mg-0.5Zr-1.8Zn-xGd bio-magnesium alloy were studied at high melting temperature (780±5 ℃). The results show that the grain size of the alloy decreases with the increase of Gd content at the range of 0-2.5wt%. The alloy without Gd is mainly composed of α-Mg and a small amount of dispersed micron Zr particles, while the alloy containing Gd is mainly composed of α-Mg and different morphologies of (Mg, Zn)₃Gd phase. The mechanical properties of the alloy increase at first and then decrease with the increase of Gd content. When the Gd content is 1.5wt%, the alloy has better mechanical properties. At the same time, the corrosion resistance increases at first and then decreases with the increase of Gd content. The uniformly distributed and fine reticulated second phase at 1.5wt% Gd content makes it better corrosion resistance. In the immersion test for 120 h, the static corrosion rate is 0.801±0.04 mm/a, and the corrosion morphology is relative uniform.