In this paper the widely concerned FD-TD method is employed in analyzing Electromagnetic scattering problems of aerocraft basic parts(square cylinder、 circle cylinder、flat board). Rectangular mesh、 effective absorbing boundary conditions and connecting conditions are used and equation of scattering data on the virtual surface which fully encloses the scatterer are obtainedAt the same time Love equivalent principle is applied to the transforming from near zone to far zone in the frequency domain, which saves much time in computing radar cross section(RCS) . And good agreement is observed between the numerical and the measured or other computed results. The method introduced in the paper helps avoid the trouble in finding the rays of diffractions and multiple reflections as compared with the high-frequency approximation--GTD and shows much better effect in solving the EM scattering problems of ultra wide band(UWB) than the methods used in frequency domain.