looihaoting:
I can obtain the RSS by plug the Arduino nano to my PC and it will be shown on serial monitor. My problem is how to obtain the RSS of the 20 lora without touching the 20 lora.
Not sure I am understanding why there is a problem or exactly what it is you are planning to do.
Just send a message addressed to each of the remote LoRa receivers and have them reply with an acknowledge, you can them read the RSSI (its not RSS) of the acknowledge reply.