Abstract: Qualitative numerical result of a special type of Coronal Mass Ejection (CME) is presented. The magnetic field direction in front half part of central closed magnetic field of the CME is opposite to that of the solar global dipole. Numerical result shows that:between the two anti-directional magnetic field lines of the CME magnetic field and the solar global dipole, there exists a transitional magnetic field structure, the area scale of which becomes gradually large when CME propagates outward. The numerical result may explain why spacecrafts can observe a type of bipolar magnetic cloud, in front half of which, the magnetic field direction is opposite to that of the solar global dipole. To obtain the numerical result, a background streamer with nested close magnetic field lines in it plays a central role for the CME initiation and propagation. The background steady state solution is approached by a long time interaction between a potential magnetic field and Parker solar wind solution. The potential magnetic field is obtained by properly combining a dipole and a hexapole. Because for the dipole, interaction between the potential magnetic field and solar wind can not open the dipole up and a streamer containing nested close magnetic field structures for triggering the CME at a suitable position forms finally.