当insist表示“坚持,坚决要求,执意”的时候,后面要跟虚拟语气,所以要加should
e.g.She insists that he should come.
她执意要他来.
而当insist表示 坚持说,固执己见的时候,不用虚拟语气,既不用加should
e.g.He insisted on his innocence./He insisted that he was innocent.
他坚持说他是无辜的.