At first, I added the following line to /etc/fstab. Then I could mount it by a command “mount -a”.
192.168.x.x:/mnt/data /mnt/nfs nfs defaults 0 0
However, it isn’t mounted on boot automatically. I searched google, and it might be a problem is that the system tried to mount nfs before networking up. To avoid this, there is a mount option “_netdev”.
192.168.x.x:/mnt/data /mnt/nfs nfs defaults,_netdev 0 0
After adding the option though it still doesn’t mount on boot. In addition, I had to enable a systemd target named “systemd-networkd-wait-online.service”, otherwise the systemd still might try to mount the nfs before networking up.
sudo systemctl enable systemd-networkd-wait-online.service
Finally it turned to be mounted on boot correctly:D.