The experiment was conducted to study the effects of dietary different forms, levels and additive time of magnesium on transportation, slaughter stress and meat quality of fattening pigs. Fattening pigs (Duroc×Landrace×Harbin) were fed corn-soybean meal cottonseed meal wheat bran as basal diet. Experiment Ⅰ or Experiment Ⅱ was randomly allocated to six replicates with five pigs in each replicate. The results showed that, serum magnesium contents in magnesium aspartate group, magnesium sulfate group, and magnesium chloride group were significantly higher than that in control group (P<0.05) ; compared with control group, the adrenaline and nordrenaline contents in magnesium aspartate group,magnesium sulfate group and magnesium chloride group were significantly lower (P<0.05). With magnesium aspartate levels increasing in the diet, serum adrenaline and nordrenaline contents were decreased, and the contents tended to become stable over 1 000 mg/kg. Compared with control group, the glycogen content of longissimus muscle in magnesium aspartate group was increased by 5.43%～12.98% (P<0.05), and also the pH was increased (P<0.05), but the lactic acid content was decreased (P<0.05) . Drip loss of the longissimus muscle in magnesium aspartate group was decreased by 45.2% compared with that in control group (P<0.05), while that of biceps in magnesium aspartate group was decreased by 2.15% compared with that in control group (P >0.05). PSE in magnesium aspartate group was decreased by 100% compared with that in control group. It was concluded that magnesium aspartate, magnesium sulfate and magnesium chloride could relieve the stress of transportation and slaughter, and the effect of magnesium aspartate was better than that of the others. Supplementation of magnesium aspartate at dose of 1 000 mg/kg not only relieved the stress but also resulted in the optimal meat color and the serum Mg levels which was increased by 11.31% before slaughter seven days ago.