In order to study the factors affecting the cleanliness of tailings of acidresistant pipeline steel, the test analysis showed that when the amount of steel remaining in the tundish was 5 and 18 t, the TO mass fraction of the last slab were 0.004 5% and 0.002 0%, respectively. When the casting speed was in the range of 0.81.5 m/min, the variation of the casting speed had little effect on the average TO mass fraction of slab, while when the casting speed was 1.51.8 m/min, the average TO content of the last slab increased obviously with the increase of casting speed. After the application of the related measures in actual production, the control effect of the last slab cleanliness was that for the first 10.7 m of the last slab for the first stop and the last stop, the highest TO mass fraction was 0.002 2%, and the lowest mass fraction was 0.001 2%, the average N mass fraction was 0.002 6%. And the fluctuation of C and S mass fraction fluctuations of the two last slabs were both small, which fully met the requirements of the HIC resistance pipeline steel. The inclusion analysis results obtained by ASPEX indicated that the number of inclusions with the diameter greater than 0.64 μm every square millimeter was 816 and 713 at the edge and center of the last slab for the first stop, and 815 and 817 at the edge and center of the last slab for the last stop, respectively.