Abstract: Three strains which belong to Orchidaceous rhizoctonias were inoculated into the tissue culture seedlings of Dendrobium candidum. They were GDB254, MLX102, CLN103 which belong to Epulorhiza sp. and Ceratorhiza sp. After 65 days, the average fresh weight of seedlings was higher than those of constrastive seedlings; the weight of seedlings, which were inoculated with the three strains were all extremely significant (α=0.01). Chloropphll a、 b content of seedlings were higher than that those of contrastive seedlings. Through observation on the microstructure of mycorrhiza. It was found that there were pelotons in cortical and vascular tissue. So it was confirmed that the relationship of symbiosis was already formed, the growth and chloropphll a、 b content of Dendrobium candidum were promoted by the mycorrhizal fungi. GDB254, MLX102, CLN103 were good mycorrhizal strains of D. candidum.