My friend's network quality is very good. It is normal to request most websites, but for individual websites.
I guess it is slow (even unable to open the page) mainly because of TCP retransmission.
I guess TCP retransmission is due to too large MTU.
Am i right？ but why PC set so large MTU?
Here are the pictures, sorry in Chinese.
Your Loopback pseudo-interface has an unusually big MTU.
AFAIS, the destination of the highlighted packet is your TP-link modem. The Source MAC address could not be identified. It generally shows the brand of your ethernet card, so it most probably is this strange Loopback device.
The problem you are facing does not seem to happen because of an unusually big MTU, I suspect this pseudo-interface is buggy, or it just blocks the website you are trying to connect to.
Disable/Uninstall this pseudo-interface and try again...