In order to reduce the computational quantity of the processing of the LFM signal in fractional Fourier domain and to meet the real-time request, a new nonuniformly sampling method is proposed. Compared to traditional nonuniformly sampling method, this method solves the problem of redundant data due to over-sampling in the whole sampling period, and eliminates the partial redundance caused by signal time-variant feature. In the end, the spectrum expression of nonuniformly sampled LFM signal in the fractional Fourier domain is derived, and the detection probability of the signal in the case of different SNR is studied. The results show that the method proposed is able to resist noise.