Preparation method of modified epoxy resin and modified epoxy resin

The invention provides modified epoxy resin and a preparation method thereof.The preparation method comprises the following steps that under the nitrogen protection condition, diisocyanate is dispersed in a first solvent at a first preset concentration, and a first solution is obtained; adding an organic solution of diamine with a second preset concentration into the first solution under a nitrogen protection condition, and obtaining a second solution under a first reaction condition; under the nitrogen protection condition, bisphenol A epoxy resin is added into the second solution, and under the second reaction condition, the modified epoxy resin is obtained. The preparation method of the modified epoxy resin provided by the invention is simple in synthesis process, and the prepared modified epoxy resin and the carbon fiber composite material produced from the modified epoxy resin have relatively high strength and toughness and have relatively good heat resistance. 本公开提供了一种改性环氧树脂的制备方法及改性环氧树脂，该制备方法包括以下步骤：在氮气保