they each 做主语时,谓语动词用复数形式,

你的提问不准确,楼上兄弟的回答也错误哈!应当说,They做主语,each做同位语时,谓语动词用复数,如：
They each put forward a proposal.（请注意each做同位语时的位置,一般置于be之后或实义动词之前）,又如：
We each have our private views about it.
如果each做主语,谓语动词一般应当用作单数,如：
Each of them thinks differet thoughts.
另,请特别注意以下两种结构：
1、each(every)+ 单数名词 + and + 单数名词,此时谓语动词用作单数,如：
Each boy and girl has come and will sign his full name before attending the ceremony.
2、each(every)+ 单数名词 + and + each(every) + 单数名词,此时谓语动词用作单数,如：
Each hour and each minute has its value.
最后,请注意,each of后的名词前须加the,如each of the soldiers（不说each of soldiers!）