The work aims to study anti-corrosion of magnesium alloy and improve its corrosion resistance. Phosphate coating on magnesium alloy was developed in electrochemical method. Single factor experiment was carried out to study the effects of current density, temperature and time on reaction process, and the best preparation scheme was obtained. Parameters including microstructure and deposition rate of the electrochemical coating on magnesium alloy were tested by means of such modern measurement techniques as X-ray fluorescence spectrometer (EDX), X-ray diffractometer (XRD) and electrochemical test, qualitative and semi-quantitative analysis results of the conversion coating constituents were obtained, and generation mechanism of electrochemical conversion coating on magnesium alloy was deduced. The optimum conditions for preparation of phosphate coating on magnesium alloy in electrochemical method were as follows: current density of 0.5 A/dm2, temperature of 30 ℃ and reaction time of 5 min. EDX analysis showed that main constituents of the electrochemical conversion coating were Mg, P, Zn, corresponding mass fraction was 11.017%, 2.105%, 28.534%, respectively. The phosphate coating consists of main constituents including Mg, P, Zn, and minor constituents such as Al, S, Ca, Mn, Ni, Cu. Corrosion mechanism is complex and uncertain. The phosphate coating of magnesium alloy mainly consists of Zn3(PO4)2?4H2O, AlPO4, MgZn2(PO4)2 and Zn, there is a small amount of other compounds as well.