The invention discloses a free-cutting Mg-Ca brass and a preparation method thereof, the Mg-Ca brass consists of copper, zinc, magnesium, calcium alloy elements and unavoidable impurities. The alloy comprises: 58-62 wt% of the copper, 0.5-3.0wt% of the magnesium, 0.1-1.5 wt% of the calcium and the balances as the zinc and the unavoidable impurities, the total content of the impurities is less than 0.1 wt%. The invention also discloses a preparation method for lead-free Mg-Ca brass. On the basis of present normal lead brass, the invention uses the magnesium and calcium elements to replace the lead element that jeopardizes environment and human body severely in consideration of main using performance and demand of the material, and meanwhile, in accordance with the requirements of environmental protection of countries all around the world, especially the developed countries, thus meeting the environmentally-friendly demand. The alloy also has excellent casting property, processing property, dynamic property, corrosion resistance and cutting property, and can take the place of the present lead Mg-Ca brass, moreover, the invention is low in manufacturing cost and can be applied to water-heating and bathroom apparatuses as well as to other various production fields.