A graded Al alloyed MoSi2/Mo5Si3 nanocomposite coating was prepared on a commercially pure titanium substrate by double cathode glow discharge. The adhesion strength of the resultant coatings to substrate was enhanced by the graded design and the formation of a wider transitional layer between the coating and substrate. Moreover, corrosion resistance of the coatings increased through the addition of Al. First-principle calculations revealed that Al additions raised the corrosion potential of both MoSi2 and Mo5Si3, and at the same time reduced the corrosion potential disparity between these two phases, thereby alleviating the occurrence of preferential corrosion.