The arbor root of Betula platy phylla was investigated in North China and the mechanical characteristics of arbor root system were quantitatively researched based on analysis of variance by using the result of root tensile test as basic data.According to the experiment al design criteria,three indexes,including rate,root length and diameter,were selected as influence factors ref lecting birch root mechanical characteristics.Four indexes,including root tensile resistance,root tensile strengt h,elastic modulus and limit extensile rate,were selected as responding factors.The results showed t hat root diameter had significant effects on root tensile resistance,root tensile strength and limit extensile rate,both root length and t ensile rate had significant effect s on elastic modulus and limit ext ensile rate.As the four responsive indexes were concerned,there w as no interact ion between rate of extensile and root length.As for tensile strength and tensile resistance,the interaction between rate of extensile and root diameter,as well as root length and root diameter both existed and had significant expressions at different levels.As elastic modulus and limit ext ensile rat e were concerned,the interaction between root length and root diameter was not significant,while the interact ion between rate of ext ensile and root diameter was significant.