The invention discloses a method for measuring residual stress of a curved workpiece using a plane wedge. The method comprises the following steps of: S1, performing ultrasonic stress test on a planeworkpiece with zero stress, collecting a measurement waveform x(n) of the plane workpiece with zero stress, and calibrating a nominal acoustic elasticity coefficient K of the plane workpiece; S2,using the plane wedge for the ultrasonic stress test of the curved workpiece to be measured, and collecting the measurement waveform y(n) of the curved workpiece; and S3,calculating a waveform delaydelta t between the x(n) and the y(n), and calculating the residual stress sigma of the workpiece to be tested as shown in the specification. L is the actual propagation distance of a critical refracting longitudinal wave in the planar workpiece. L is the actual propagation distance of the critical refracting longitudinal wave in the curved workpiece. Delta t is the acoustic time difference caused by the difference in propagation time between ultrasonic waves in the wedge and a coupling layer due to the different geometrical structures of the planar workpiece and the curved workpiece when using the plane wedge to perform the ultrasonic stress test on the planar workpiece and the curved workpiece. The method is simple, fast, low cost, and has high precision.