Hi.
Wich library is used to the communication between two RF modules?
Wire??
And when I send a character (for example ' A ') from a module to another, the character arrived is encoded to ' 每 '
HELPPP
That depends on what the modules are.
Some use Wire, some use SPI, some use RS-232 (UART)...
First step: read the data sheet for your module.
Start here
Is it the 315 MHz or 433 MHz modules? If so you will need the VirtualWire library.