人称代词里的：主格放在句首做主语和表语,宾格放在句末或句中做动词和介词的宾语.
打个比方，主人邀请宾客，主格就像主人，宾格就像宾客。主格在动词前面，宾格在动词或介词后面。
英语中的人称代词(Personal Pronouns)有主格、宾格和之分，如：
I, me, my ; he, him, his ; they, them,their等。
顾名思义，主格(The nominative case)用作主语，宾格(The objective case)用作宾语，所有格(The possessive case)则表示所有之物。
在实际运用中，主格和宾格代词有时会混淆。下面是常见的问题：
⒈在复合结构里，人称代词的主格和宾格在单独使用时，没有问题，如很少人会犯下这样的错误：
*(1)Wilcox spoke to I.
*(2)Her knew what had happened.
但在复合结构中，错误就难免了，如：
*(3)Wilcox spoke to my friend and I.
*(4)He and her knew what had happened.
*(5)This is between you and he.
这种错误是可避免的。第一，在有介词的复合结构中，特别要注意，第二个人称代词，必须用宾语，如："for you and me"和 "between Maria and him"。第二，试把复合结构中的另一部分暂时用括号围起来，那么该用的格就容易辨别了，如：
(6)This message is for (My father and) I or me.
(7)(Marry and) he or him went downtown together.
显然的，(5)里的代词是宾格的"me", (6)里的代词是主格的"he"。
⒉在比较结构里，连接词"as"或"than"后面，按理用主格式，但在口语中，人们常用宾格形式，学美式英语者，更是如此：
(8)a. You did as well as she.
b. You did as well as her.
(9)a. I am older than he.
b. I am older than him.
(a)和(b)两种说法，都可接受。但如果"as"和"than"后头分句的主语和词动都要完整出现的话，这时的人称代词，就必须是主格，如下：
(10)You did as well as she did.
(11)I am older than he is .
此外，还有一点要注意，就是"as"和"than"后面虽然在语法上用主格好，用宾格也可，但是有时意思会有所不同。试比较(a)和(b)：
(12)a. Jason praised Maria more highly than I.
b. Jason praised Maria more highly than me.
(12)a和b都被接受，但(12)a等于(13)a，而(12)b等于(13)B：
(13)a. Jason praised Maria more highly than I did (= I praised Maria).
b. Jason praised Maria more highly than he praised me.
显然，这两句的深层意思大有差别。遇到这种情形，为了避免误解，不妨根据要表达的意思用完整的句式表达出来。换句话说，必要的话，要用(13)这句子。
不然，把(13)a变成(14), (13)b变成(15)也可：
(14)I did not praise Maria as highly as Jason did.
(15)Jason did not praise me as highly as he praised Maria.
参考资料：http://zhidao.baidu.com/question/2869972.html?fr=qrl3