In the traditional reliability model , the probability density function of random variable is important . so , in chapter 2 , the methods to get probability density function of engineering random variable are discussed . three methods , which include approximate method , monte - carlo simulation method and multiple parameter method , are compared by some examples . in chapter 3 , some non - probabilistic reliability models are discussed 在傳統的概率可靠性模型中,變量的概率密度函數的確定非常重要,因此在本文第二章中,主要著力討論工程隨機變量概率密度函數的求解方法,說明原理,推導求解公式,并通過實際算例對近似解析法、 monte - carlo數字模擬法、多參數法三種方法進行對比。