Abstract: Dose calculation parameters, including dose rate constant, radial dose function and anisotropy function, were calculated by using Monte-Carlo simulation (MCNP) for model CS-1 ¹³¹Cs interstitial brachytherapy seed, in order to elusidate the discrepancy in the present parameter data. The calculated result of dose rate constant is 1.055 cGy•h^-1•U^-1, showing excellent agreement with that of Chen et al., 1.066 and 1.058 cGy•h^-1•U^-1, determined by gamma spectrometer and thermoluminescent dosimeter (TLD) respectively. According to recommendation of TG43U1, radial dose function was calculated and complemented in the range of 0.1 to 10.0 cm, as well as anisotropy function in the range of 1.0 to 7.0 cm and 0° to 90°. Empirical equations were acquired for radial dose function and anisotropy function by curve fitting.