The formation of high T_c phase is very sluggish and c parameter of unit cell of high T_c phase is about 37Å. High T_c oxide superconductor with a T_c above 100K has been successfully prepared by solid state reaction method in BiSrCaCuO system by Pb adding. The microstructure related to the formation of the high T_c phase has been investigated. As compared with YBCO compound, the formation reaction of the high T_c requires long time heat treatment. It is due to the transformation from the low T_c phase to high T_c phase. The sintering just below the melting point of the calcined powder mixture is effective on the formation of the high T_c phase in Pb-added BiSrCaCuO system. The growth of the high T_c superconducting phase has a thin plate shape, which is characterized by the c parameter of 37Å. The formation of the high T_c phases is delayed by the excessive addition of Pb. The lattice parameter (c) of the unit cell (both the low and high T_c phases) is increased with increase of Pb.