Why my iPhone X auto update,but screen show “iPhone will restart when update complete”..

Hi there Haiwang1126,

Welcome to Apple Support Communities. We can understand the concern with your device not updating, and we're happy to help. You can find the steps to resolve this issue here:

If your iPhone, iPad or iPod touch won’t update

And if you have access to a Mac or Windows PC with iTunes installed, you can use the computer to get your device updated. Follow the guidance here to do so:

Update your iPhone, iPad, or iPod touch

Let us know if you have any questions.

Best regards!