Generally, we will first think that it is a DNS problem. You can try to use ip to access a server (website) and see if the downlink does not work. If it does not work, then it should not be a DNS problem. Or change the DNS, such as 114, or the DNS required by your own intranet.
If the above attempts still do not work, try the following methods:
1. Open System Preferences—>Network—>WiFi—>Advanced—>WiFi—>Delete all networks in the Preferred Network box—>Click OK—>Click Apply;
2. On the network page first, there are WiFi, Bluetooth PAN, bridge, etc. in the border, select WiFi, click the minus sign below to delete WiFi, and click Apply;3. Finder—>xxx Mac—>Macintosh HD—>Resource Library—>Preferences—>SystemConfiguration—>Find the NerworkInterfaces.plist file and delete it;
If you can't find the Mac or Macintosh HD of xxx , press command+ on the finder page to enter the following page, select "Sidebar", and tick your mac or macbook. Then you can see the relevant ones on the left side of the finder.
If it still doesn't work, there is the final ultimate move: command+option+p+r, press and hold when booting, and release when you hear more than 3 beeps. Specifically, you can search Baidu for the meaning of this command. It is to completely reset the controller, but it does not affect the hard disk data and does not need to be backed up.