The invention discloses a method for preparing modified wheat gluten protein by decarboxamidation and organic acid. The method comprises the steps: the organic acid is dissolved in 5 to 15 percent (w/w) of wheat gluten protein suspension, the mass concentration of the organic acid in the wheat gluten protein suspension is 0.2 to 1.5 percent; the solution reacts at a temperature of 110 DEG C to 126 DEG C for 5 to 30 minutes and is cooled and diluted for 5 to 10 times before small molecular acid residue is removed by ultrafiltration, and the solution is condensed, sprayed and dried to obtain the modified wheat gluten protein. The method has simple production technology, low protein hydrolysis degree, high safety and strong feasibility of implementation, and the final product has high foamability and can be used for baking and swelling food.