In this paper， a 2FSK modulation and demodulation system is designed and implemented based on Quartus13.1 using the hardware description language verilog for digital modulation and demodulation of digital baseband signals in digital communication.The frequency divider is used to obtain different carrier frequency， the pseudorandom sequence is used to generate baseband signal， key frequency shift method for signal modulation， zerocrossing detection signal to achieve the baseband signal. The entire system of a modular design verification gets the right function， no error 2FSK modem. And the 2FSK modem is applied to the ultraviolet laser communication system after several tests,the system reaches the beam incident angle of the distance of 50m， the system can realize the extremely low rate communication with the error rate of 10-4 and the communication speed of 600bps