Abstract: Aiming the upwarping in the inner wall after TP304L stainless steel pierced，the organization of upwarping samples were analysied by high magnification electron microscope. The result shows that the main reasons for the formation of cracks on the inner wall is the lath ferrite, and th elath ferrite is due to solidication mode. The question was solved after the solidification mode was adjusted from FA mode to AF mode.

Key words: TP304L stainless steel, upwarping, organization, ferrite, solidification mode