A substrate polishing method includes a stock polishing step comprising a plurality of stock polishing sub-steps in which a first polishing solution, a second polishing solution, and a third polishing solution are applied, in that order, to a substrate. A content COMP1 of water-soluble polymer P1 in the first polishing solution, a content COMP2 of water-soluble polymer P2 in the second polishing solution, and a content COMP3 of water-soluble polymer P3 in the third polishing solution satisfy COMP1