本文採用達成機率來衡量投資風險之觀念，針對建築投資具有多階段的銷售特性，發展一套數學解析模式，來計算各銷售階段之階段變數可能的組合，所產生之達成機率及相對應之經濟報酬率，以建立整體達成機率與經濟報酬率之機會集合。同時在風險考量下，推導各階段變數之可能組合的限制範圍，以便能較簡捷地尋求最大經濟報酬率與整體達成機率的決策組合，作為建築投資決策之參考。

　　　　　This paper investigates the problem of investment risk and economic return for a building project using the concept of upside risk. An analytical model of opportunity set is constructed, based on the characteristics of the phased building sales. This model can calculate each opportunity set of the investment risk and its associated economic return, which is produced by a decision portfolio of each sale phase. Besides, under the consideration of the risk status, the limited range of a possible portfolio of each sale phase can be set up. Therefore, the optimal portfolio of a building investment can be found efficiently.