The invention discloses a method for preparing lignin ester by mechanical activation-solid reaction. The method comprises the following steps of weighing reaction materials according to the ratio of lignin to an acylating agent to a catalyst is 15g: 0.08-0.6mol: 0.15-6.7g; placing the reaction material in a ball mill; performing thermostatic waterbath at the temperature of 50-90 DEG C; stirring at the low rotating speed of 100-500 r/min and performing acylation for 0.5-4 hours to obtain crude products of the lignin ester; separating the crude products from pellets; placing the crude products of the lignin ester in solvent and standing to separate out solid; separating the solid from the solvent by filtering; and removing the acylating agent and the catalyst by using a solvent repeated washing and filtering method or an extraction method to obtain lignin ester products. The lignin ester is synthesized by mechanical activation-solid synthesis, the shortcoming that activity of chemical reaction of lignin is low is overcome, and problems existing in preparation of the lignin ester by the traditional liquid-phase method are solved. The method has the advantages that the method is pollution-free and low in cost; reaction materials are mixed fully; equipment cost is low; energy consumption is low; reaction time is short; modified lignin is easy to recycle; a producing and preparing technology is simplified; and the method is easy and convenient to operate.