當系統或製程屬於相當複雜的情形時，影響正常運作之主因往往不易發覺。在實際狀況無法掌控時，工程師便引入機率的觀點來判斷系統本身具有的特性，藉由特定且連續之曲線來適當描述系統的失效機制，可靠度模型便由此衍生而來。因此在不同的失效率函數中，從參數的改變觀察其可靠度模型之特性，乃為本文的重點所在。 從可靠度理論的介紹可知，機率密度函數之特性與失效機率函數息息相關，因此我們可以從機率密度函數之特性了解不同分佈之趨勢，藉由機率密度函數分析的結果研究特定可靠度模型之特性，深具探討意義。 When systems or processes are complicated, the major cause which affects the operation is usually not easy to find. Engineers take advantage of the viewpoint of probability to analyze the characteristics of systems. Reliability models can describe the failure behavior of systems in the particular and continuous form. Hence the observation of characteristics of the reliability models is the main point in this paper through the variation of parameters in particular hazard rate function. It mentions that probability density function is related to the hazard rate function in the definition of reliability. We can understand the trend of different distribution by analyzing the characteristics of probability density function. It is significant to research the features of particular reliability models by the discussion of probability density function.