[Solved]Raspberry Pi connect with Pixhawk

Hello everyone, I have a problem.
I just follow a tutorial like this http://ardupilot.org/dev/docs/raspberry-pi-via-mavlink.html
When I type the command “param show ARMING_CHECK”, it no any response.
But I using RC Radio to change flight mode, the terminal will show the changed.

Can anyone help me please.

The problem just be solved.
It just downgrade the pymavlink version.
And it can work now.