Abstract: In order to explore the morphology characteristics of the laser welded joint of Ti6Al4V alloy under low vacuum environment, non-penetration welding was performed under 5 Pa ambient pressure. The influence law of laser power and defocus amount on the weld morphology was studied, and the stability and formation interval of the typical joint morphology were analyzed. The results show that the weld bead quality can be obtained by changing the process parameters in a wide range under low vacuum ambient pressure, and the weld penetration increases linearly with the increase of output power. The geometric features of welded joints can be divided into two types: the U shape formed when the line energy utilization factor is less than 0.13 or greater than 0.14, and the V shape formed when the line energy utilization factor is between 0.13 and 0.14. V shape keyhole stability is poor, it is difficult to maintain the quasi steady state, weld penetration depth fluctuation is large, easy to form defects at the bottom of the weld.