Squarified layout algorithm is widely used in the Treemap Visualization, but classic Squarified algorithm cannot achieve the best average aspect ratio. By analyzing implementation details of Squarified Treemap layout algorithm, especially each step of the rectangular block position selection process, the paper demonstrates the drawback of classic Squarified algorithm caused by using greedy algorithm. Combining with depth-first search technique, it also proposes Squarified Treemap layout algorithm based on depth-first search (DSS algorithm). Based on elaborating implementation process of DSS algorithm, combining empirical research, the advantage of the DSS algorithm in the aspect ratio, the improvement direction and the essential characteristics of the time performance are discussed.