1.启动sqlplus 

2.请输入用户名:  sqlplus/as sysdba 

3.输入口令: 直接回车 

4.连接到: 
   Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production 
   With the Partitioning, OLAP, Data Mining and Real Application Testing options 
   SQL>alter user sys identified by admin; 
  用户已更改。 
  SQL> conn sys/admin as sysdba; 
  已连接。 
  SQL> alter user system identified by manager; 
  用户已更改。 

Oracle 11g忘记sys、system、scott密码该这样修改！