The work aims to improve corrosion and wear resistance of AZ91HP magnesium alloy and expand its application scope. H3PO4+Na3PO4 pickling solution and NH4HF2 activated chromium-free pretreatment process was utilized and then electroless plating was performed to obtain Ni-P coating. Later heat treatment was done to the coating. Characterization analysis of morphology, microhardness and corrosion resistance of the substrate and coating before and after plating was performed. Small and compact cellular structures of good adhesion were formed since the AZ91HP magnesium alloy was plated after receiving chromium-free treatment of H3PO4+Na3PO4 pickling solution and NH4HF2 activation. The coating was mainly amorphous. The corrosion resistance was higher than that of the substrate. After heat treatment, microhardness of the coating increased significantly and was the highest at 400 ℃, but the corrosion resistance decreased slightly. The system of H3PO4+Na3PO4 pickling and NH4HF2 activation provides an environmental-friendly and efficient pretreatment process for magnesium alloy. Ni-P alloy coating mainly in amorphous state was obtained, which has improved corrosion resistance of the substrate, and microhardness of the coating could be further improved by heat treatment.