复杂句和复合句都有两个句子组成，复合句中，两个句子独立表达完整的意思，能独立存活。复杂句由一个主句和一个从句组成,其中的从句不能独立表达一个完整的意思。

复合句

复合句分为并列复合句（也称并列句）和主从或从属复合句（也称复杂句）。

Beijing is in the North and Nanjing is in the South.

特点：When two independent clauses, or complete sentences are joined together, they form one compound sentence.

复合句是由两个独立的句子组合在一起构成的。例句中，有下面两个完整并且独立的句子组成：

Beijing is in the North.

Nanjing is in the South.

复杂句

复杂句，某个句子成分直接由从属分句表示，那么这种句子便不是简单句而是复杂句。

My uncle, who is seventy years old, works on a farm.

特点：When an independent clause and a dependent clause are joined together; they form one complex sentence.

复合句是由一个独立的句子加一个从句构成的。

China is a country that its history is very long.

China is a country.(独立句子)

That its history is very long(从句)