Abstract: The determination has shown that the increase and reduction in content of iron and manganeses in leaf are consistent with that in the soil. Sand culture and water culture added evidence that the increase of content of watersoluble iron was the major cause in decline and withering of the root system and the main factor which depressed the uptake of manganese. When the soil was poorly aerated, the situation was more serious. The high rate of water content in soil was the main infective condition by faeultative parasite in Oomycetes for descending axis of Cunninghamia lanceolata which was hence hastened to death.