be good at 中的at是介詞。

因為介詞後面只能加上名詞或者動名詞形式，所以be good at 後面應該接名詞或者動名詞形式。例如：I am good at dancing.我擅長跳舞。My mother is good at drawing.我的媽媽擅長畫畫。這兩句中的dancing和drawing都是動名詞形式。I am good at English.我擅長英語。這裡的English就是名詞的形式。

be good at的at是介詞,後面可以接名詞，代詞和動詞ing形式，短語的意思是擅長於...。

1.Fishing is good at high water.高水位有利於釣魚。

2.He is good at charming money out of companies.他擅長利用自己的魅力從各家公司套錢。

3.Keller is good at describing music – an almost impossible task to do well.凱勒擅長描述音樂——這可是一項幾乎難以做好的任務。

4.She is good at the art of painting.她擅長繪畫之道。

be good at / be good with /be good to / be good for

be good 後接不同的介詞,表達的意思也不同.

1）be good at 意為“擅長……”,後接名詞、代詞或ving形式.例如：

I’m good at playing chess.

我擅長下象棋.

2）be good with意為“靈巧的；與……相處得好”=get on well with.例如：

She is good with her hands.

她手很巧.

He is very good with the children.

他與這些孩子處得很好.

3）be good to意為“對……友好”.例如：

My friend was good to me when I was ill.

我生病時我的朋友對我關懷備至.

4）be good for意為 “對……有好處”.例如：

Eating more vegetables is good for your health.

多吃蔬菜對你的健康有好處.