Abstract: The formation mechanism,distribution,number of pores and the effect of welding parameters in TIG welding of MGH956 alloy sheet were studied by X-ray method and metallurgical analysis. The results show that pores in MGH956 alloy TIG welds is related to fabrication technology of the alloy MGH956 and the microstructures in the weld. Pores are inclined to distribute linkly near the fusion line,due to the characteristics in the different sections of weld pool,the microstructure and distribution of temperature in the weld joint. Optimizing welding parameters can affect the number of pores. Low heat input such as low current,high speed and appropriate pulse frequency can reduce the number of pores to some extent.