The invention discloses a method for preparing a monophenol compound through catalyzing degradation of lignin by using an ammino-complex. The method comprises the steps: adding the lignin, a metal salt, ammonia water, a peroxidant, an alkali and deionized water into a high-pressure reaction vessel, and carrying out stirring to form a uniform solution; carrying out a reaction for 100 to 240 minutes at the temperature of 120 DEG C to 180 DEG C, and carrying out cooling; and adjusting the pH value of a reaction solution to 2 to 3 with an acid, then, carrying out a reaction for 10 to 20 minutes at the temperature of 100 DEG C to 120 DEG C, carrying out cooling, then, carrying out filtration to collect filtrate, carrying out extraction on the filtrate with dichloromethane, separating an organic phase, and carrying out drying with anhydrous calcium chloride, thereby obtaining a monophenol compound mixed solution. According to the method, a stable ammino-complex solution is formed by using the metal salt and the ammonia water under alkaline conditions, so that the number of sites of contact between a catalyst and the lignin can be effectively increased compared with that in the conventional lignin oxidative degradation method; the degradation of the lignin can be efficiently catalyzed in an aqueous solution under moderate reaction conditions; and the method has the characteristics of high efficiency and low cost and is applicable to large-scale industrial production.