This paper presents a simulation model for uranium series geochronological dating employed in adjusting the age of the earth claimed by evolutionary scientists. The model assumes that decay half-lives have been constant throughout earth history, but introduces detailed equations to simulate diffusion and migration of radionuclide through a porous medium. Theoretically, a radiometric-dating model should be developed based on the solute transport theory, which involves tedious numerical computation. However, the traditional model imposes two crude assumptions to simplify the computational processes, even though it is known that inevitable errors may result. They are: (1) mineral deposits are confined in a closed system and no radionuclide migration can take place, and (2) the decay chain is in its "ultimate" equilibrium at the time of dating. On the other hand, the proposed simulation model calculates the age of minerals based on the solute transport theory. As such, the errors inherited in the traditional model can be minimized or avoided. The results of model verification indicate that there are excellent agreements between the simulation results and the analytical solutions for two cases: radioactive decay and diffusion. Comparison of the results indicates that the closed system assumption results in overestimation of the age of mineral when the age exceeds the "critical year." A comparison of an existing study for a rhyolite from the Cobb Mountain, California and results from the simulation model also show the same trend.