A new procedure is proposed to generate planar asymmetric coronas with multi-streamer structures, as shown in SOHO/LASCO observations. The initial coronal magnetic field is separated into potential part and non-potential part. We first fit the potential part by using the sum of magnetic multi-poles, whereas the non-potential part is approximated by the magnetic field induced by some properly fitted current densities. Then the total field is numerically modified in terms of Maxwell's equations. Based on the initial magnetic fields obtained in such a way, we can further compute various complex asymmetric corona structures by solving MHD equations. In order to verify this procedure, we compute the 2-D coronal structures prior to the December, 1996 CME and August, 1999 CME events. The numerical result is on the whole in agreement with observations, and hence set proper backgrounds for further studying the propagation of CME in various coronal structures using numerical computations. ¿ 2001 American Geophysical Union