She can not understand anything but know how to keep my heart hurt.有没语法错误.

She can not understand anything but know how to keep my heart hurt

基本没有什么错误，但是去掉know更好，否则似乎有点落索。

有，句子很啰嗦。可以改成这样：
She knows nothing but how to hurt my heart.
或者：
She understands nothing but how to hurt my heart.
不过第一个句子会比较好。

有。正确的说法是
She knows nothing but how to hurt my heart.

can not 有点错误吧
She don't understand anything but know how to keep my heart hurt

每个人翻译的时候不必要非简练，有些啰嗦的句子在某种语境下能起到表白者更深层的心意。按照你的逻辑思维来翻译的话，我的建议是：

She couldn't understand anything but she knows how to keep my heart hurt.

\两种改法
1，把hurt改成hurting
2，how to hurt my heart.
当然，两种改法中Konw都是要去掉的