C:\Users\dong>sqlplus/nolog
SQL*Plus: Release 11.2.0.1.0 Production on Mon Nov 19 14:12:51 2018
Copyright (c) 1982, 2010, Oracle. All rights reserved.
SQL> conn / as sysdba
ERROR:
ORA-12560: TNS:protocol adapter error
SQL>
更改windows环境变量，服务端路径载前客户端路径在后，然后重启系统