The results on testing the decay resistance of Pinus Yunnanensis heartwood rotted in different levels with mediums of malt-ager, sand, soil and wood decay fungi (Coriolus Versicolor and Lenzites trabea) as well as the cells structural change of wood punky were reported. The results showed that the decay resistance of rotten timbers increased with the decrease of decay degrees. The observation of scanning electron microscopy indicated that the more hyphae penetrate holes in the cell walls, the higher decay levels of timber.