Abstract: According to dose calculation formalism recommended by AAPM TG43U1, dose rate constant, radial dose function and anisotropy function of Model 6711(3M) ¹²⁵I brachytherapy source are calculated by Monte-Carlo method. Comparisons with relative data recommended by AAPM are performed. Dose rate constant, 0.986cGy·h^-1U^-1, within 2.31% compared to recommended value of TG43U1; values of radial dose function are in good agreement with TG43 and TG43U1; the agreement of anisotropy function with TG43 and TG43U1 is improved with increase of angle and distance. Experiential equations are obtained for radial dose function and anisotropy function by curve and surface fitting.