Abstract: The white dot defect occurred at the butt girth weld of a certain steel pipe. The causes of white dots were studied by macroscopic observation, mechanical property testing, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that before welding, the weld groove was not fully dried and the hydrogen ion content in the weld was too high, led to the aggregation of hydrogen ions and the formation of white dots. Improper welding operation resulted in non-metallic inclusions not precipitated in time and non-metallic inclusions were generated inside the white dots.