Thanks for your helping, this is really a happy thing!
I run this command
$ source <ws>/install/setup.bash before run ‘$ rosrun rosserial_python serial_node.py tcp’. Then, the problem is solved.
And I also tried to run ‘$ rosrun rosserial_python serial_node.py tcp’ directly, it did occurred the same errors. That means I should to run that command everytime.
Thus, I run this command in a new terminal
$ echo "source catkin_ws/install/setup.bash" >> ~/.bashrc. Then, I won’t have to run this command everytime.