本文以Barro (1990)、Turnovsky (1997)與Lai and Liao (2012)的模型為基礎，建構一個小型開放經濟的內生成長模型，為凸顯資本市場移動性所扮演的角色，分別探討政府當局在面對資本完全移動及資本不完全移動時，該如何制訂一套最適之非線型所得稅以追求社會福利極大。根據本文的分析，可得出以下結論： 一、在資本完全移動的情況下，為矯正政府基礎建設的生產外部性，可透過課徵所得稅矯正市場失靈的扭曲，並利用累退稅率矯正因所得稅尺度所造成資本邊際生產力過低的扭曲。政府可以透過最適租稅結構矯正所有分權經濟體系的扭曲，使得經濟體系達到最佳境界的經濟成長率與福利水準。 二、在資本不完全移動的情況下，當最適的所得稅尺度等於基礎建設的生產外部性，矯正了基礎建設的生產外部性，並且透過累進／累退稅率矯正課稅後導致資本邊際生產力過低的扭曲，然而代表性個人在做最適決策時視國外利率為固定，總體決策中利率會隨著借債規模而變動，存在資本不完全移動性的扭曲，經數值模擬的結果得知，代表性個人相對社會最適借債過多，因而無法使得經濟體系達到柏拉圖最適境界。 / Based on the Barro (1990), Turnovsky (1997) and Lai and Liao (2012) model, this thesis specifies that on endogenous growth model of a developing economy facing an upward-sloping supply curve of debt. The analysis includes both perfect world capital market case and imperfect world capital market case. The government’s infrastructure expenditure is financed by nonlinear income taxation, and examine how the fiscal authority devises its nonlinear tax structure from the viewpoint of welfare maximization. Several main findings emerge from the analysis. First, in a world of perfect capital market, it is found that a suitable package containing two instruments can fully remedy the inefficiencies arising from the production externality and distortionary taxation, as a result, the Pareto optimality can be restored. Second, according to the calibration results, in the face of imperfect world capital market, there are three distortions in the economy: the production externality, the capital externality, and the financial externality association with the upward-sloping supply of debt. Two policy instruments for the tax scalar and tax progressivity/regressivity causing the distortion arising from the production externality and the capital externality to vanish. Consequently, one remaining distortion, namely, the financial externality association with the upward-sloping supply of debt, are present in the economy. As a consequence, the structure of the optimal tax policy that won’t permit the attainment of the first-best optimum.