Abstract: Prompt gamma activation imaging (PGAI) is a new type of element distribution imaging method in a non-destructive way. At present, the PGAI measure platforms which have been completed are all applied under the ideal model, and only for analyzing small pieces of sample by using the neutron source at the reactor. To discuss the accuracy and validate the feasibility of PGAI technology based on cold and thermal neutron, the ideal model of PGAI was analyzed by using Monte Carlo software. A homogeneous sample of 5 cm×5 cm×1 cm which consisted of pure iron was measured by adopting collimated neutron beam and the high-purity Ge detector, the dimension of the isovolume was 1 cm×1 cm×1 cm. It is shown that two kinds of energy neutrons all has been successfully used in PGAI. But no matter what kind of energy neutrons, when measuring the homogeneous single element sample, the consistency of image reconstruction results can't be guaranteed because of the neutron self-absorption, neutron scattering and γ-ray self-absorption. Therefore we need to analyze the physical mechanism and establish proper correction model in our later work.