I can remotely login into a sun WS with solaris9 installed by ssh. The connection command is as follows:

1#xhost +
2#ssh -X My_ID@Remote_Server_IP or Name

After login, I tried to start xterm but the following error is shown me:

3# xterm &
xterm XT error: Can not open display.

Because I want to use some cad software in another Pc I wonder some methods to solve the remote display problem.
Please help me!

Hi -

Off the top of my head, the first two things to look for might be:
1. Do you have a firewall between your PC and the Solaris host, and
2. If so, are X-windows ports 6000/tcp and 177/udp open?

I'm assuming that you already have an X windows emulator (such as eXceed or Cygwin/X) installed and operational on your PC. Can you open and display an X11 app (such as XClock) locally on your PC?

'Hope that helps ... PSM

Yes, I have installed Cygwin in my win pc and I can start the X11 application such as Xclock. But I do not know how to confirm if there is a firewall between my winpc and sunpc. If assuming not , how to confirm if the 6000/tcp and 177/udp is open.

This is not a firewall issue, as you are able to communicate with ssh, and X11 protocol is tunneled in the same ssh connection.
The issue may be due to sshd on the Solaris side not allowing X11 tunneling.
check is X11Forwarding is set in /etc/ssh/sshd_config

Also, the error message "xterm Xt error: Can't open display: "
shows the DISPLAY variable is not set, it should be set on the calling shell (the one that call "ssh -X ...", and on the target machine, it should be something like ":10" to work.

Another reason would be for the ssh key having change, in that case there is this message "X11 forwarding is disabled to avoid man-in-the-middle attacks."
displayed at login time.