The snapshot image mapping spectrometer (IMS) has advantages such as high temporal resolution,high throughput,compact structure and simple reconstructed algorithm.In recent years,it has been utilized in biomedicine,remote sensing,etc.However,the system errors and various factors can cause cross talk,image degradation and spectral distortion in the system.In this research,a theoretical model is presented along with the point response function (PRF) for the IMS,and the influence of the mirror tilt angle error of the image mapper and the prism apex angle error are analyzed based on the model.The results indicate that the tilt angle error causes loss of light throughput and the prism apex angle error causes spectral mixing between adjacent sub-images.The light intensity on the image plane is reduced to 95％ when the mirror tilt angle error is increased to ± 100" (≈ 0.028°).The prism apex error should be controlled within the range of 0-36" (0.01 °) to ensure the designed number of spectral bands,and avoid spectral mixing between adjacent images.