This paper presents a frequency domain input impedance model for three phase diode rectifier. Compared to literature work, this model has two significantly better features: (1) it is valid in a wide frequency range, which is from below fundamental frequency to more than 30 times of fundamental frequency; (2) it considers the effect of the ac line impedance and output dc impedance, by setting them as variables in the model; in another word, these impedance can be arbitrary value as long as the circuit works in continuous mode. It is tested that the model is still accurate even when the output filter inductor becomes zero. At different circuit parameters, including the extreme cases, the analytical modeling results and the numerical simulation results present excellent agreement, which demonstrates the accuracy of the analytical model. The resulting model is intended for stability analysis in a large ac power system involving significant number of rectification loads. Detailed derivation of the model is presented in this paper, and numerical simulation measurement results are also presented to validate the results.