Abstract: The disease of Chinese fir [Cunninghamia lanceolata (lamb). Hook. ] familiarly known as "Big Head Disease" found in shaowu, Fujian province was proved to be a physiological disease caused by boron deficiency by means of optical microscope inspertion, electronic microscope analysis. Transplantation, grafting , exploratory control, elemental analysis and fertilization. Results of correlation between disease rate and environment factors such as soil, climate in different nurseries have showed that the disease develops easily in acid, light soils with low organic matter and boron contents. High temperature and drought could aggravate the disease all the more. Furthermore the root-shoot ratio measurement showed that the diaeased plant has low root-shoot ratio, and this was thought to becaused by inner boron deficiency in the Chinese fir.