Since the digital mircomirror device (DMD) is working in slant optical path in the coded aperture imaging spectrometer, the coded pixel will generate unsymmetrical distortion on detector, which will make it unable to determine the coded method corresponding to each pixel of obtained coded image when decoding. In order to solve this problem, this paper proposes a method of "unsymmetrical deformation regular stripe calibration". Through the changes that the regular stripe produces on the detector, the deformation of the coded pixel is visually observed. According to the known stripe rule, the deformation of the image can be quantitatively analyzed and corrected. This method can ensure the correction of the coded image under the premise of clear imaging of the entire field of view of the system. Firstly, the imaging principle of the designed spectrometer and the deformation reason of the coded pixel are introduced. Secondly, the detector is adjusted during the experiment to obtain a full-clear field of view. Finally, the proposed method is used to process the coded image. Experiments show that the similarity between the processed image and the theoretical value is 37.87% higher than that of the unprocessed image. The image restores the pattern shape loaded by the DMD, which lays the foundation for the next decoded operation.