搞了百度一下才知道，原来是表锁住了！
查出哪些对象被锁：
select a.*,b.* from v$locked_object a,dba_objects b where b.object_id = a.object_id
查出锁住对象的session ID 和serial#：
select ,,#,t2.logon_time
from v$locked_object t1,v$session t2
where t1.session_id= order by t2.logon_time
杀死session：
alter system kill session 'ID,Serial#'