When abroad，he often dreamed of his hometown. 

这里的abroad是副词吗？

【答】这里的 when 是连词，引导时间状语从句； abroad 是副词，在从句中作表语，意思是“在国外”。

如果 when 引导的时间状语从句的主语和主句的主语相同，可以把从句的主语和谓语中的 be 动词一起省略。所以：

When he was abroad, he often dreamed of his hometown.  = When abroad，he often dreamed of his hometown.