Abstract: Retention functions and dose coefficients derived from some biokinetic models vary a lot. Crawford-Brown model has the unique advantage of describing chemical forms transfer of tritium and analyzing dose coefficients of different age groups. In this article, several important biokinetic models of tritium were introduced. Crawford-Brown model was especially analyzed, age-specific dose coefficients were calculated and the results were discussed. The results show that HTO and OBT dose coefficients derived from Crawford-Brown model are larger than that from the ICRP model in all age groups except for the adult group. As the age is smaller, the difference of the two models is more obvious because of the transfer of HTO and OBT. The comparison in adult retention functions of HTO ingestion shows that retention functions in the first 100 d are almost exactly the same, while the long retention terms are significantly different.