Morinda officinalis polysaccharide is an important bioactive substance, in terms of its anti-depression, immune enhancement, anti-viral and anti-tumor effects, and polysaccharide holds great potential in function food and drug development. In this study, the Box-Behnken design principle and one-factor-at-a-time experiments were employed to optimize the extraction parameters of polysaccharide from Morinda officinalis How in Deqing area, Guangdong province. The in vitro antioxidant activities of extracted polysaccharides were also investigated. The results showed that the optimal extraction conditions were as follows: extraction time was 2 h, extraction times was 3, and solid-liquid ratio was 1∶11 （g/mL）. Under the control of these conditions, the polysaccharide yield of Morinda officinalis was 6.71%, which was only less 0.11% than the theoretically predicted value. The obtained Morinda officinalis polysaccharides have a potent O^-₂· and DPPH· scavenging capacity, indicating that the optimized process conditions were stable and feasible. The blood urea nitrogen (BUN) and arterial blood lactate concentration (LACT) were decreased while the hepatic glycogenosis (HG) was increased after treated with different concentrations of polysaccharides of Morinda officinalis How in NIH mice, which indicates that the polysaccharides of Morinda officinalis How has anti-fatigue in vivo.