Abstract: Due to the high fusion temperature and large thermal capacity,the pure titanium always has coarse grain which makes poor properties of welded joint.In this paper the structure of welded joint was improved by micro-alloy transition,and the alloy phase and microstructure were analyzed.The results showed that for different welding procedures,proper alloying can refine the structure and grains of commercial pure titanium welded joint.In terms of the distribution of structure,the basic microstructures of welded joint were α,γ and strengthening particle TiB2,and the eutectic phrase α'might appear under the condition of rapid cooling.The thin needles TiB2 existed at grain boundary with the forms of cruciform,T shape and the composition of cruciform and T shape.