Hi everyone:
I run this command like below, it works for me.

i make a dir name uct and run this command(composer create-project --repository=https://repo.magento.com magento/upgrade-compatibility-tool=3.0.17 ./ -vvv), it works for me. Download uct successfully!

I just curious about why it is works specify the uct`s version and -vvv parameters. But in magento office documents, it tell developer to run like below:

Anyway , i am able to go futher step to use uct finally!