Moso bamboo (Phyllostachys pubescens) linear-vibration welded joints with three different combinations between the inner and outer surfaces were studied in this paper. The tensile-shear strength, the microstructures and welded layer thickness observed by SEM and the density profiles measured by X-ray densitometer of the welded samples have been considered and compared. The maximum average tensile-shear strength of outer-outer, inner-inner and outer-inner welded joints were 5.91, 7.15 and 6.24MPa, respectively. And only the inner-inner welded joints have the bamboo failure after the shear test. The welded joint is composed of a lot of bamboo fibers entangled in the molten and flown intercellular materials which decide the final mechanical performance of the welded joints. The thickness of the outer-outer welded layer is the smallest and the inner-inner welded layer is the highest. However, the maximum density reached in the inner-inner welded joint is smaller than in the outer-outer welded joint owing to the different vascular distribution in the cross section of the moso bamboo. The relative density can be used to reflect the tensile-shear strength of the welded joints. The natural structure of bamboo really do have significant influences on the welded interface.