In this paper a dynamic food chain model for Hong Kong which simulates the transfer of radioactive substances from a fallout deposition via the food chain into the human bodies is built. The model is based on the RADFOOD model and the Birchall-James algorithm. The radionuclides ¹³¹I and ⁹⁰Sr representing the short-term and long-term risk situations have been studied as sample cases. Various types of crops, and the dietary pattern of the public have been considered. The resulting internal radiation doses have been calculated. The results are obtained for food consumption starting at various time after the fallout deposition and for different consumption durations.