区别就是surround back是动词surround的动副短语但意思是不一样的，具体的不同如下

surround 中文意思是v. 围绕，环绕（军队，警察等）包围与……紧密相连（或相关）喜欢结交（某类人），身边总有（某类东西）

surround back中文意思是向后环绕

When his children saw their father back， they all also followed and surround him.