declare @t varchar(255),@c varchar(255) 
declare table_cursor cursor for 
select a.name,b.name from sysobjects a,syscolumns b ,systypes c 
where a.id=b.id and a.xtype='u' and c.name in (--这里是要替换的类型 
'char', 'nchar', 'nvarchar', 'varchar','text','ntext' --这里如果你的text(ntext)类型没有超过8000(4000)长度，才可以使用
) 
declare @str varchar(500),@str2 varchar(500) 
--这里是你要替换的原字符 
set @str='aa' 
--这里是你要替换的新字符 
set @str2='bb'
open table_cursor fetch next from table_cursor into @t,@c 
while(@@fetch_status=0) 
begin 
    exec('update [' + @t + '] set [' + @c + ']=replace(cast([' + @c + '] as varchar(8000)),'''+@str+''','''+ @str2 +''')') 
    fetch next from table_cursor into @t,@c 
end 
close table_cursor 
deallocate table_cursor;