Abstract: To take further the advantage of the solute-rich surface layer of twin-roll cast high-P steel strip, the causes for the formation of the P-rich surface layer were discussed. Experimental results indicated that there will be a P-rich layer nearby the surface of the higher-P strip after controlling the processing parameters, but the distribution of phosphorus is basically uniform in the lower-P strip under the same conditions. Theoretical analysis showed that the rolling force may drive the interdendritic P-rich liquid metal back onto the strip surface, thus resulting in the formation of the P-rich layer in the strip under the preconditions that the kiss point takes place above the bite and the cross-section temperature of the nearby region below the kiss point is between the liquidus and solidus temperature.