这里的that是代词,“那件事或者那个东西”的意思,在句中作said的宾语。整个句子的意思是“他说那件事情,就好像他到过那里似的”。这里不要把that当成是引导宾语从句的引导词,形式上像,但实际上不是。
He said that as if he had been there.
句子结构不对呀。
that引导的宾语从句结构不完整。
可以改为:He said that it seemed as if he had been there.
或者:He felt as if he had been there.