Bamboo as a kind of fastgrowing plant has so similar properties as those in wood,and so often to be used as wood.As a sort of natural engineering and building material,the physical and mechanical properties of bamboo wood were affected by the moisture content in the culm.The fiber saturation point of tree wood has been studied and defined for over a century.However,the relation between moisture content and physical and mechanical properties of bamboo wood had hardly been illustrated.Knowledge of the relation between properties and moisture content in bamboo is the basis for further understanding of the plant and its properies,for putting them to proper uses and processing.In this paper,the shrinkage rates of radial and tangential dimensions in Dendrocalamus hamiltonii under different moisture content was tested and the reasons causing differences between bamboo and tree wood in tangential and radial shrinkage by comparing the distinctions of their anatomic structure were analysed.With the curve fit model method,the cubic equation is adopted to fit the experiment data resulting in a good effect.According to the equation and testing figure,the critical point in the curve was found out and was further defined as fiber saturation point(FSP).The FSP values derived from the radial and tangential shrinkage in D.hamiltonii were 34.84% and 34.52% respectively.