1.a bit与a little都可作程度副词,表示"稍微、一点儿"的意思,修饰动词、形容词、比较级等,二者可以互换.例如：
Will you please turn down the radio a bit/a little?(动词)请你把收音机声音关小一点好吗?
She's a bit/a little afraid of the teacher.(形容词)她有点怕老师.
Her mother feels a bit/a little better today.(比较级)她母亲今天感觉好一些.
2.for a bit和for a little意思相同,相当于for a while或for a short time,可互换.例如：
Let's rest for a bit/a little.让我们休息一下.
II.不同之处
1.a little可以直接修饰不可数名词,而a bit修饰不可数名词时,只能用a bit of.例如：
Tom has a little money./Tom has a bit of money.汤姆有一点钱.
但是,当a little修饰的名词前有this,that,所有格等限定词时,也要用a little of结构.例如：
I want to drink a little of that drink.我想喝点那种饮料.
2.a bit和a little与not连用时,意思大相径庭.not a bit＝not at all,意为"一点也不"；not a little＝very much,意为"十分"、"相当"、"极其".