'express' is not an internal or external command, nor is it a runnable program, or batch file

1. npm install -g express-generator to install the new express
framework Can't get the order?

The version of nodejs is: v6.11.0 The
version of npm is: 3.10.10
I check the system environment variables:
The path of my nodejs is: C:\Program Files\nodejs\
express-generator The installation version path is: C:\Users\vigor \AppData\Roaming\npm

Question: Why is my global installation not below the directory for npm under nodejs?
Reference: https://blog.csdn.net/suiyuehuimou/article/details/74143436
According to the document prompt:
execute npm config get prefix
Feedback: C :\Users\vigor\AppData\Roaming\npm
It turns out that I have set the directory to this place.
Then the documentation should configure an environment variable just fine.