Abstract Based on the analysis of continuous casting slab soft reduction process, a expression to calculate soft reduction efficiency was deduced, and the effects of soft reduction amount and liquid core thickness on reduction efficiency were investigated. The results show that the reduction efficiency increases linearly with the increase of liquid core thickess as reduction amout is the same, and as the reduction amount is bigger than 2.3mm, the relationship of reduction efficiency η and reduction amount △H can be expressed by η=-0.00902+0.01155△H. For the same thickness of liquid core, the increase of reduction amount will induce the increase of reduction efficiency as reduction amount is less than 2.3mm, while the reduction amount has little effect on reduction efficiency as reduction amount is bigger than 2.3mm.