The invention discloses a non-linear frequency-modulated signal undersampling processing method. The method comprises the following steps of step1) using a sampling frequency which is lower than a radar system emission signal st(t) bandwidth to carry out AD undersampling on a radar echo signal s(t) after a down-conversion to base band process; acquiring an undersampling echo signal sp(t); step2) in a digital domain, carrying out frequency mixing on the undersampling echo signal sp(t) and a de-sloping digital reference signal and acquiring a de-sloping digital signal sd(t); step3) carrying outupsampling on the de-sloping digital signal sd(t), carrying out linear frequency modulation on the signal after upsampling and a reference linear frequency modulation signal to recover a broadband echo signal sm(t); and step4) carrying out matched filtering on the recovered broadband echo signal sm(t) and the emission signal st(t), and then carrying out pulse compression to acquire a target one-dimensional distance image. By using the method of the invention, when a distance between a radar and a mapping range is small, broad-band non-linear frequency-modulated signal undersampling processingis realized, simultaneously, a system sampling rate is reduced, and a data transmission quantity and a storage amount are decreased.