1. on the decline在减少中，在下坡路上，在逐渐衰退
Thankfully the smoking of cigarettes is on the decline
令人欣慰的是，吸烟量在逐渐下降。
His prosperity is on the decline.
他的好光景日见衰败。
His father is on the decline.
他父亲的身体越来越弱。
The forces of imperialism are on the decline.
帝国主义的力量正在逐渐衰退。
In our town, interest in sports is on the decline.
在我们这个镇，对体育的兴趣正在降低。
But before they can be assured, more efforts must be made, because the population of the crane in the wild is on the decline, and many other species appear headed toward extinction.
它们得到保护之前需要我们做更多努力，因为野生鹤的数量正在下降，许多其他物种也似乎正在走向灭绝。高考真题
2. in decline在衰落中，走向衰落，在没落中
Inflation is rampant and industry in decline.
通胀势头严重，工业不断下滑。
He is still one of the world's most popular golfers, but his game is in decline.
他仍是世界上最受欢迎的高尔夫球选手之一，但他的球技日不如前。
The customs are in decline.
风俗凌夷。（风俗日渐式微。）
With his life in decline, he waited for death.
他生命垂危，他只有等死了。
Fish stocks in the Baltic are in decline.
波罗的海的鱼类资源逐渐减少。
3. in the decline of在……后期，在……晚期
in the decline of life 晚年