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Based on ammonia recycled percolation (ARP) and combined with the advantage of ammonia fiber explosion (AFEX), a set of reflowed aqua ammonia explosion pretreatment (RAAEP) equipment was developed. According to the previous orthogonal experiment experimental results, the optimal pretreatment conditions were at 90°C, 9 min retention time, water to dry corn stover loading of 0.8:1(w/w), and aqua ammonia flow rate is 1.5L/min. The cellulose content of the pretreated corn stover was 50.46 % and the glucan and xylan enzymatic digestibility was 86.45 % and 95.77% respectively. The reflowed aqua ammonia not only caused fiber swelling and an efficient delignification (up to 62.5%) of biomass, but also altered the cellulose crystalline structure. The SEM picture and FTIR spectra confirmed swelling and significant delignification effects of the RAAEP process. The X-ray crystallography data indicated that the rigid structure of corn stover was disrupted with more crystallization fiber being exposed after the pretreatment process, but the crystallinity increased due to the removal of amorphous materials (lignin and hemicelluloses).