Could you show the whole section of the log that does the connection? From the part where it says:

Log opened at 2019-01-29 14:50:58

to where it says:

Log closed at 2019-01-29 14:50:58

And please don't leave out anything.

Secondly, can you provide the raw HTTP request and response headers, with a tool such as Chrome's or Firefox's dev tools?

When visit http://localhost/, xdebug can not work properly, the log is:
Log opened at 2019-01-30 01:55:51
I: Checking remote connect back address.
I: Checking header 'HTTP_X_FORWARDED_FOR'.
I: Checking header 'REMOTE_ADDR'.
I: Remote address found, connecting to ::1:9000.
E: Time-out connecting to client (Waited: 200 ms). :-(
Log closed at 2019-01-30 01:55:51

When visit http://127.0.0.1/, xdebug work properly, and the log is:
Log opened at 2019-01-30 01:59:03
I: Checking remote connect back address.
I: Checking header 'HTTP_X_FORWARDED_FOR'.
I: Checking header 'REMOTEADDR'.
I: Remote address found, connecting to 127.0.0.1:9000.
I: Connected to client. :-)
-> <init xmlns="urn:debugger...
extra log..

The different is ip, when visit localhost the ip is ipv6 while 127.0.0.1 is ipv4

The php plugin of idea binds socket using ipV4, when I run netstat -nao | find "9000" in cmd:
C:\Users\clu>netstat -nao | find "9000"
TCP 0.0.0.0:9000 0.0.0.0:0 LISTENING 10964

So if xdebug connect to ::1:9000 (IPv6), it can not connect successfully, but is connect to 127.0.0.1:9000 (IPv4), it is OK.

I have tried to change the config in php.ini:
from
xdebug.remote_host = localhost
to
xdebug.remote_host = 127.0.0.1

but it has no effect...
so, I just need a config for xdebug as follows in php.ini
xdebug.prefer_ipv4_stack = true
then it can connect to the debug server by 127.0.0.1:9000 when I visit http://localhost.

or make the config xdebug.remote_host = 127.0.0.1 become effective

You wrote:

I have tried to change the config in php.ini:
from
xdebug.remote_host = localhost
to
xdebug.remote_host = 127.0.0.1

but it has no effect...

That makes sense, as this setting is ignored when you have xdebug.remote_connect_back turned on. So turning off remote_connect_back should solve this problem.

Xdebug uses the Operating System's mechanisms (getaddrinfo()) to convert and Xdebug does look at all returned matches for a specific name. On correct setups, that would include the IPv4 and IPv6 variants.

However, in:

I: Remote address found, connecting to ::1:9000.

We see that your browser doesn't send over localhost in the HTTP headers, but instead uses "::1" which means that Xdebug can't do its own name resolving from "localhost" to both IPv4 and IPv6 variants.

In any case, turning off xdebug.remote_connect_back (setting it to =0) should do the trick for you.

is this now resolved for you?

yes, thanks...

Thanks for letting me know. I'll close this issue then.