但是OAS不就是已经剔除了Option Cost的Spread吗？那Option cost变化对OAS也会有影响吗？

Ok, I see the problem, the definition of OAS we talk about are not the same.

The OAS I learned is the total spread of an asset it is callable, prepayable, whatever. While the static spread is the spread that there is no prepayment. OAS-static spread=option value.

But I check the website and find some definitions are the same as you mentioned. I think the definition on your book is the same is that in my knowledge. The market qoutes OAS because it reflects the real return the inverstor can get. So if the OAS is the one that subtracts the option's value, I don't think it makes much sense.

啊？！居然有这么严重的问题啊……晕，这么重要的概念居然这么不严谨……好吧，我再看看，谢谢你的解答：）

Chemist_MZ 讲的是正解。两个概念非常正确。