Processing bamboo fiber by rolling bamboo is a main methods in bamboo fiber making. However, present the basic research for making bamboo fiber by rolling are rarely work. In rolling method, plastic property of bamboo and rolling force are important factors.In this paper, strength property variation of moso bamboo with different moisture content after alkali treatment were studied. Based on the HILL-Tsai Strength theory,the yield condition of bamboo under rolling load was found. The research provided a theoretical basis to found mechanical model of rolling method in bamboo fiber making.