Abstract: A method for calculating the prompt dose of Uranium Processing and Fuel Fabrication Facilities under nuclear criticality accidents based on MCNP code modeling was established, and the analysis and comparison was done with the calculation method stipulated in criteria EJ/T988-96. Then took a fuel research and development site at home as an example, the prompt dose of public on the edge of site was calculated. The results showed that the prompt dose in a nuclear criticality accident was overvalued using the calculation method stipulated in criteria; The modeling method based on MCNP made the calculation result more accurate because of its scientific algorithm, accurate description of shielding medium and controllability of the result error. Therefore, it is suggested that the MCNP-based code modeling method be used to assess the prompt dose under the nuclear criticality accidents of Uranium Processing and Fuel Fabrication Facilities.