Abstract: This paper discusses the treatment of bagasse black liquor in alkalescent condition. The suitable adsorption and flocculation conditions were as follows: bentonite 120 g/L, dicyandiamide–formaldehyde 6 mL/L, reaction temperature 40 ℃，fast stirring time 2 min and clarification time 25 hours. It was found that N, K and lots of lignin were present in the adsorption and flocculation mud, which could be used as the raw material to prepare organic solid fertilizer. The clarified black liquor could be recycled as the process water.