The invention provides a digital processing device for improving the FSK modulation characteristic of a direct phase locking frequency modulation emitter. A filtering and buffering module receives an external digital base band signal lock fs and an external digital base band signal, and the external digital base band signal lock fs and the external digital base band signal are filtered and buffered by a shift register and then output to a frequency doubling module and a coding module respectively; the frequency doubling module receives a lock filtered by the filtering and buffering module, a phase-locked loop in the frequency doubling module performs frequency doubling on the lock, and then a frequency-doubled lock nfs is output to the coding module; the coding module receives a digital base band signal filtered by the filtering and buffering module and outputs a coded digital base band signal to the voltage tuning end of a voltage-controlled oscillator in the direct phase locking frequency modulation emitter, so that FSK modulation is achieved. By means of the digital processing device, the direct phase locking frequency modulation emitter can perform FSK modulation on low-bit-rate digital base band signals without limitation of the bandwidth of a loop filter.