The digital modulation is necessary in order to meet the requirement of higher signal transmission rate in aerocraft data link. The better modulating performance and the longer communication distance can be achieved by digital modulation. The principle of 2 Continuous Phase Frequency Shift Keying(CPFSK) modulation with binary continuous phase is introduced. A 2CPFSK quadrature modulation algorithm based on software radio architecture is proposed. By using the phase accumulation property of 2CPFSK, the algorithm realizes the fractional interpolation of baseband data to adapt to the modulation of wide range code rate. A digital filter is also designed to improve spectral purity. The hardware platform of digital modulator based on Field Programmable Gate Array+Digital-to-Analog Converter(FPGA+DAC) architecture is designed and the algorithm is implemented. Compared with traditional analog Frequency Modulation(FM), this design improves the link performance by 1.7 dB and increases the communication distance of the system.