In the prompt gamma activation imaging, the neutron self-shielding and gamma self-absorption effect inside the sample will cause uneven distribution of the measurement results. To solve the problem of the biased distribution in the prompt gamma activation imaging, the influence of the neutron field inside the sample and the self-absorption effect of gamma were studied, and the transport process of neutrons and gamma rays was theoretically deduced. A mathematical model for correcting the biased distribution and image reconstruction was established. The Monte Carlo method was used to simulate the prompt gamma activation imaging of Fe and H elements, and the mathematical model was used to reconstruct the element images. The results show that the influence of neutron self-shielding and γ self-absorption effect in prompt gamma activation imaging has been significantly corrected, and the content distribution of Fe and H elements can be accurately reconstructed using this mathematical model, which verify the validity of the mathematical model.