The invention relates to the field of radar signal processing technology and particularly relates to a radar digital signal processing method and a device thereof. The basic principle of the radar digital signal processing method and the device thereof is that: time sharing processing is conducted to intrapulse sampling data of the linear frequency-modulated interruptive-continuous wave radar to separate original signals which have distance aliasing in the frequency domain by time, and then the separated signal spectrum is recombined to be restored to a spectrum form that has no distance aliasing. The method, differing from traditional methods that only use FFT to obtain an A-type spectrum, conducts the time sharing processing to intrapulse echoed signals. The method is characterized in that the A-type spectrum having no distance aliasing can be obtained from signals having distance aliasing and the range resolution can be increased.