Al ion plating was carried to improve corrosion resistance of Nd-based permanent magnet made by prwder molding method. The effects of applied votage, pressyre and temperature were investigated to find the reation between coating parameters and their properties. Density of coating layer increased with voltage and thus corrosion resistance improved. However when voltage was applied more than 1000V, corrosion resistance whet down because of resputtering effect. Good corrosion resistance was acquired when gas pressure was $5.0 imes10^-2$>torr, which is satisfied momentum energy of Ar, Al ions as well as quantity of plasma. The layer coated in low temperature range have better surface density and corrosion resistance than in high temperature. This result is seemed due to the characteristics of substrate itself. All coating layers were showed stong adhesion with substrate.