For all who is following this,
I've found the tutorial: Tutorial: IoT Datalogger with ESP8266 WiFi Module and FRDM-KL25Z | MCU on Eclipse
I can now communicate with Thingspeak. But there are somethings really weird! The wiring is still the same. But I change the way of command:
(My firmware version is: 00170901)
(already connected to access point)
AT+CIPMUX=0
AT+CIPSTART="TCP","184.106.153.149",80
AT+CIPSEND=46
GET /update?key=xxxxxxxxxxxxx&field1=50
the serial monitor did not respond until I sent the "AT" command to check if it was alive! So funny that, the ESP responded:
busy s...
SEND OK
+IPD,1:2
OK
OK
Unlink
And the data of Field 1 in my Thingspeak channel is changed to 50, exactly what I want.
But I cannot explain anything about this. Does anyone have anything more about this?