本文以直接模擬蒙地卡羅法(Direct Simulation Monte Carlo Method)來模擬研究三維微結構物理模型對流場現象與熱傳作分析與探討。在低速管流的模擬中，紐森數的範圍設定在0.08到1.8之間且微結構溫度分別設定為273K，323K和373K。在模擬中，比較三維模擬結果與二微模擬結果之差異性。就結果而言，可以觀察出在三維模擬的例子中，兩側壁的效應影響了熱傳與流場性質且在三維的流場模擬中，壁的熱傳量也隨著紐森數的增加而減少。而在三維的模擬中，也模擬加大長寬比1，3和5倍，其結果顯現在三維的模擬中，長寬比小於3的時候，兩邊壁的效應對熱傳與流場的影響就相當顯著。隨著長寬比的增加，此時流場的性質與熱傳表現是接近二維模擬時的結果。當長寬比大於5的時候，發現二維模擬的結果是合理的。 The Direct Simulation Monte Carlo (DSMC) method is employed to analyze the heat transfer and the fluid dynamics characteristics of a 3-D microstructure. The microchannel flows are simulated with Knudsen numbers ranging between 0.08 and 1.8 and with three different temperatures 273k, 323k and 373k of microstructure. The calculated flow properties in the 3-D case are compared with those in the 2-D case. It shows that the two extra side walls in the 3-D case have significant effects on the heat transfer. The wall heat transfer decreases with an increase in Knudsen number. The 3-D microchannel flows is also simulated with the cross aspect ratio in the range of 1 ,3 and 5. It shows that when the aspect ratio < 3, the two extra side walls in the 3-D case have significant effects on the heat transfer. When the aspect ratio increases, the flow pattern and heat transfer characteristics tend to approach that of 2-D results. The 2-D simplification is found to be reasonable only when the cross aspect ratio is larger than 5.