这里引用alwaysever此前在百度知道给出的解释,在此对原创表示感谢.
一.instead意为“代替”“替代”,作副词用,通常位于句尾.如位于句首时常用逗号与后面阁开.instead 在顺接句子中作“代替”讲,而在转折（或逆转）句子中作“然而”讲.
例如：1.Lily isn't here. Ask Lucy instead.
Lily不在这儿,去问Lucy吧. [注意]当instead在祈使句中时,只能位于句末.
2.she didn't answer me, instead, she asked me another question.
她没有回答我,反而问了我另外一个问题.
二.instead of是介宾短语,其意与instead相同,不同之处在于它后面常接宾语,起宾语多由名词、代词、介词、短语、动词 + ing 形式充当.
例如：1.We'll ask Li Mei instead of Mary.
我们将去问李梅而不问玛丽.
2.I'll go instead of her.
我会替她去.
三.instead 与instead of的转换.
例如: 1.He didn't answer me, instead, he asked me another question → He asked me another question instead of answering me.
2.I'll go instead of her.→She won't go.I'll go instead
