近年来，中学数学刊物和数学竞赛题中经常出现大量新颖的三元对称分式不等式．其证明方法也较独特巧妙，如利用均值不等式、柯西不等式、排序原理等．它们一般不易被中学生想到或接受．为此，笔者在教学中向学生介绍了证明不等式的原始方法——作差比较法，结合恒等变形，构造 In recent years, a large number of novel ternary symmetrical fractional inequalities often appear in middle school mathematics publications and mathematic competitions. The method of proof is also unique and ingenious, such as using mean inequality, Cauchy inequality, sorting principle, etc. They are generally not easily thought or accepted by middle school students. For this reason, the author introduces students to the original method of proving inequality in the teaching - the difference comparison method, combining the constant deformation, constructing