This paper introduced a method of specimen preparation for electron microscopy which showed the ultrastructure of the infection threads in the host cell of Robinia pseudoacacia. Based on the specimen preparation of TEM, thick sections and ultrathin sections were made at the same location on nodule embeded by Epon_812. Thick sections were de_resined and coated with gold_palladium for SEM; ultrathin sections were stained for TEM. The result showed specimens prepared by this method could obtain ultrastructrue image and three_dimensional image at the same location while infection threads in the host cell of Robinia pseudoacacia.