As biomedical materials, magnesium alloys have a wide application prospect due to their excellent biocompatibility and biodegradability. Effectively improving corrosion resistance of magnesium alloy was of great importance to biomedical materials. PSS/PAH multilayer films were prepared on the surface of AZ31 substrate based on layer-by-layer assembly by virtue of dip-coating method, then the modified samples were hydrothermal treated in the solution of Ca(NO)3, NaH2PO4 and Na2CO3 to induce the formation of Ca-P coating (HA). The surface morphology and chemical composition of the films were characterized by using high resolution scanning electron microscopy, Fourier infrared spectrometer and X-ray photoelectron spectroscopy. Hydrogen evolution and electrochemical experiment (including potentiodynamic polarization and electrochemical impedance spectroscopy) were conducted to study corrosion resistance of Ca-P/(PAH/PSS)5/Mg coating. The Ca-P coating was approximately 7.67 μm thick, in presence of leaf-like shape, randomly and densely arranged on the alloy. With Ca-P/(PAH/PSS)5/Mg coating thickness increased by one order of magnitude, the corrosion current density decreased from 3.69×10–5 to 1.61× 10–6 A/cm2, so did the hydrogen evolution rate. The corrosion resistance of the magnesium alloy can be im-proved effectively by the Ca-P coating, which can be ascribed to biological mineralization of the two assembled polyelectrolytes. The Ca-P coating obtained by induction provides a new idea application of magnesium alloy in biomedical field.