The influence of casting speed variation on non-metallic inclusions in surface layers of IF steel slabs during continuous casting were investigated with OPA (Original Position Statistic Distribution Analysis) method. It was found that, when the casting speed was evenly decreased from 1.4 to 0.6 m/min, increases of the nonmetallic inclusions owing to the increase of the mold powder entrapment were observed only on those slabs which were cast at the start of casting speed change. While, in experiment of increasing casting speed evenly from 0.6 to 1.4 m/min, increases of nonmetallic inclusions were observed only on slabs which are cast at the time when the casting speed was stopped to increase after it had been increased to 1.4 m/min. For slabs which were cast during the casting speed evenly increasing or decreasing period and at the time when increasing or decreasing the casting speed at low casting speed level (0.6 m/min), the influence of casting speed change was very small. In addition, it was found that, at high casting speed level (1.4 m/min), even a little change of casting speed could result in remarkable increase of the non-metallic inclusions. Thus, at high casting speed, changing casting speed should be avoided or using much slower speed changing rate.