本文所稱之策略性成本結構乃指當既存廠商欲阻止潛在廠商進入市場時，成本結構的策略性管理，而所謂成本結構即是廠商的變動成本與固定成本組成之比例。成本結構的策略性管理乃是加入市場上產品替代程度的考量，廠商選擇最適成本結構，以維持在市場的競爭優勢，來阻止潛在廠商進入市場。本文自策略性成本觀點，來探討當產品替代程度變動時，固定成本與變動成本問之策略性結構。研究結果顯示：當既存廠商欲阻止潛在廠商進入市場時，策略性成本結構的特徵是變動成本隨固定成本遞增而遞減，且遞減率呈遞減。當產品替代程度下降時，既存廠商會偏重固定成本經營策略，以強化規模優勢。當產品替代程度增加時，既存廠商會偏重變動成本經營策略，以追求成本彈性或加強取得高品質的生產要素。在較容易阻止潛在廠商進入的情況下，替代程度增加，造成固定成本減少得越多。至於產品替代性與潛在廠商的相對需求優勢對既存廠商利潤的影響，需視阻止潛在廠商進入的難易情況而定。 In this paper, an incumbent firm to deter potential entrants uses the strategic cost structure, defined as a method of managing costs. Cost structure is the ratio of variable cost to fixed cost strategic cost structure means the strategic choice of cost structure of the incumbent firm. In order to maintain its competitive advantage, the incumbent firm chooses the best strategic cost structure to keep its potential entrants from entering the market. From the viewpoint of strategic cost structure, we will examine the choice between variable cost and fixed cost when the degree of product substitutes changes. This paper shows that the incumbent firm's variable cost decreases along with an increase of its fixed cost when it tries to deter entry, and the marginal decreasing rate decreases. The incumbent would focus on the fixed cost strategy to create the scale advantage if the degree of product substitues is low. When the degree of product substitues is high, the incumbent would focus on the variable cost strategy to enhance the flexible advantage of it costs or to obtain better quality of production factors. When it is easier to deter entry, then the increasing degree of product substitutes makes fixed cost increase more. Furthermore, effects of product substitutes and absolute advantages on the incumbent's profit depend on the difficulty of entry.