[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.

2016/10/18
The problem just be solved.
It just downgrade the pymavlink version.
And it can work now.