Well,there is something interesting now.
It suddenly occurred to me that maybe I should change another WIFI connection. So I tried my smart phone hotspot. this time it does work.Both PMDG and fenix can request data from simbrief appropriately.
However, when I checked the ping as you just mentioned. I found it was even slower than my original Wi-Fi.
In a way, it did solve my problem by changing Wi-Fi.
Thank you anyway