The work aims to improve the corrosion resistance of magnesium alloy by preparing phosphate-permanganate conversion coating on the surface of magnesium alloy. The chemical conversion coating on the surface of magnesium alloy was prepared with phosphate-permanganate as conversion electrolyte. Effects of conversion temperature, pH value and conversion time on the surface morphology, chemical composition, thickness, structure and corrosion resistance of the conversion coating were studied by scanning electron microscopy (SEM), energy dispersion analyzer of X-ray (EDAX), X-ray diffraction (XRD) and electrochemical test. The phosphate-permanganate conversion coating was dark violet and 4~18 μm thick. It consisted of Mg, P, Mn and O elements with purple appearance and micro cracks. The corrosion resistance of conversion coating first increased and then decreased as the conversion temperature, pH value and conversion time increased. The phosphate- permanganate conversion coating is composed of magnesium phosphate. Optimum processing conditions are as follows: conversion temperature of 40 ℃, pH value of 3.5 and conversion time of 20 min. After chemical conversion treatment by phosphate-permanganate conversion electrolyte, the corrosion resistance of magnesium alloy is greatly improved.