In this paper,an 8 mm thick TC4 titanium alloy thick plate was used as the experimental material. Under the test conditions of two kinds of welding methods:manual tungsten inert gas arc（TIG） welding and metal inert-gas arc（MIG）welding,the similarities and differences of formation of weld,microstructure,mechanical properties and tensile fractures were studied. The results show that both TIG and MIG have good formation of weld,but the MIG welding speed is faster;the base metal is α+β dual phase microstruc-ture,the grain of the MIG welding heat affected zone is more uniform than that of TIG welding. Both welds are composed of thick columnar crystals,and the microstructure is α’ martensite +β phase. The strength coefficient of manual TIG welded joint is 97.3%,and the strength coefficient of the oscillating arc MIG welded joint is 93.9%. The reason for the low strength of the oscillating arc MIG welding is the existence of blowhole defects in the weld.