A reliability test method based on cyclic frequency features was proposed to evaluate the blind processing results of linear frequency modulation (LFM) signal.The reference signal was constructed depending on the identified modulationtype and the correspondent parameters estimations at first and the correlations between the observed signal and the reference signal were calculated consequently.The reliability for LFM signal processing result was tested by detecting the presence of cyclic frequencies near zero frequency of the correlations.The theoretical error probability of the detection was derived and the case study for the discrete polynomial transform (DPT) method was described in the paper.Simulation results show that the proposed algorithm avoids estimating of signal-to-noise ratio and is superior to the time domain based method under lower signal-to-noise ratios.