When private sector participates in public construction project, it involves with high technical risk and has to bear heavy financial risk. The financial risk contains many uncertain variables and is easily affected by the macro-economic development. Consequently, the risk enlarges the gap between the actually executed and the originally planned. And even, it profoundly influences the later development of the overall construction project. The purpose of this paper is to present a study result that tried to minimize the gap. The study was based on the actually executed financial data and model used in Taiwan High Speed Rail BOT Project. After prudent analysis and synthesis, the result demonstrates that the depreciation method and the value of assets after completion of the project have significant impact on the finance ratios of the BOT project. Therefore, a suggestion is made that government should pre-formulate effective measures on the definition of investment scope and the options of investment items for private sector's participation when a BOT project is initiated.