Abstract: The best uniform rational approximation combined with method of moments (MoM) is proposed to quickly calculate the three-dimensional radar cross section (RCS) of complex arbitrary shape object in spatial domains. Compared with the asymptotic waveform evaluation (AWE) technique, the Maehly approximation does not require the complex computation concerning dense impedance matrix, and it is accurate in much broader range. It can be easily implemented into an existing MoM computer code. Compared with the results calculated at each frequency using MoM, the proposed technique is found to be superior in terms of the CPU time. Good agreement between the proposed method and the traditional MoM is observed. Numerical results show that the proposed method is available.