Abstract: The peanut meal was fermented by Bacillus natto to prepare nattokinase. The technological conditions were optimized by single factor and orthogonal experiments with a primary indicator of nattokinase. The results showed that the optimal conditions were as follows: fermentation temperature 37 ℃,inoculum size 10%,the ratio of solid / liquid 1∶ 0.4 g / m L,fermentation time 24 h.Under the optimized conditions,the activity of nattokinase reached3162 U / m L,18% higher than that obtained in one-factor-at-a-time experiments( only 2680 U / m L). And soluble nitrogen reached 5.6 mg / m L. Hydroxyl free radicals scavenging activity of fermentation broth was 74%,and the required absorbance for determining iron reduction capacities was 0.906.