A multi-layered porous plug comprising: an upper porous part having a plurality of pores formed therein and is configured to blow an inert gas comprising argon (Ar) or nitrogen injected into molten steel; a lower porous part having a plurality of pores formed therein, and provided under the upper porous part, and make the inert gas pass through to the upper porous part; a porous indicator part 3 having a plurality of pores formed therein, and provided under the lower porous part 2, and having a sectional shape different from that of the lower porous part so that whether the porous part remains can be checked at a position above the upper porous part; and a sleeve part configured to surround the upper porous part, the lower porous part and the porous indicator part; wherein a bottom width of the upper porous part is larger than a top width of the lower porous part, wherein the upper porous part has a first sectional shape, and the lower porous part has a second sectional shape different from the first sectional shape, wherein a length (L1,L2) of each of the upper porous part 1 and the lower porous part is 100 mm to 250 mm, wherein the sectional shape of the upper porous part is circle, and the sectional shape of the lower porous part is rectangular, and the sectional shape of the porous indicator part is circle, wherein the lower porous part further comprising a first concave part provided upper side and a first stepped part provide on the outer portion of the first concave part, wherein the porous indicator part further comprising a second concave part provided upper side and a second stepped part provide on the outer portion of the second concave part, wherein the porous indicator part further comprising a third concave part provided center of lower side and a third stepped part provide on the outer portion of the third concave part, wherein the upper porous part, the lower porous part, the porous indicator and the sleeve portion has a structure in which width increases toward the bottom, wherein the vertical length of the upper porous part 1 is longer than the vertical length of the lower porous part, and the vertical length of the lower porous part 2 is longer than the vertical length of the porous indicator part. an upper porous part having a plurality of pores formed therein and is configured to blow an inert gas comprising argon (Ar) or nitrogen injected into molten steel; a lower porous part having a plurality of pores formed therein, and provided under the upper porous part, and make the inert gas pass through to the upper porous part; a porous indicator part 3 having a plurality of pores formed therein, and provided under the lower porous part 2, and having a sectional shape different from that of the lower porous part so that whether the porous part remains can be checked at a position above the upper porous part; and a sleeve part configured to surround the upper porous part, the lower porous part and the porous indicator part; wherein a bottom width of the upper porous part is larger than a top width of the lower porous part, wherein the upper porous part has a first sectional shape, and the lower porous part has a second sectional shape different from the first sectional shape, wherein a length (L1,L2) of each of the upper porous part 1 and the lower porous part is 100 mm to 250 mm, wherein the sectional shape of the upper porous part is circle, and the sectional shape of the lower porous part is rectangular, and the sectional shape of the porous indicator part is circle, wherein the lower porous part further comprising a first concave part provided upper side and a first stepped part provide on the outer portion of the first concave part, wherein the porous indicator part further comprising a second concave part provided upper side and a second stepped part provide on the outer portion of the second concave part, wherein the porous indicator part further comprising a third concave part provided center of lower side and a third stepped part provide on the outer portion of the third concave part, wherein the upper porous part, the lower porous part, the porous indicator and the sleeve portion has a structure in which width increases toward the bottom, wherein the vertical length of the upper porous part 1 is longer than the vertical length of the lower porous part, and the vertical length of the lower porous part 2 is longer than the vertical length of the porous indicator part.