In present work, the wetting behavior of Al-Mg alloys with different Mg amount (3.2, 4.5, 6.5, 8.5, 10, 13, 17 wt.% Mg) on M40 graphite fabrics was investigated by sessile drop method. The effect of Mg amount on the wettability and spreading behavior were discussed. The initial contact angle decreased from 115o in Al-3.2Mg/graphite fabrics to 88.5o in Al-17Mg/graphite fabrics system. The final contact angles decreased from 96.7o in Al-3.2Mg/graphite fabrics to 71o in Al-17Mg/graphite fabrics system. The initial contact angle measured on porous M40 graphite fabrics was lower than reported results on dense carbon plates due to the surface microstructure of M40 fibres. Due to surface tension decrease of Al-Mg alloys, the initial and final contact angles decreased with increasing of Mg amount. According to Dezellus equation, the kinetic constant (k) in spreading behavior was obtained from data fitting of experimental results. Miedema model was introduced in present work to calculate the theoretical k. The experimental or theoretical k changed little with increasing of Mg amount. Moreover, theoretical calculation values of k are very close to the experimental results, which indicate the applicability of Miedema model to the calculation of kinetic constant.