Information entropy is an important technology to measure information of the signal. Considering the Digital Radio Frequency Memory(DRFM) jamming detection for pulse compression radar, a method of DRFM jamming detection based on information theory is proposed, by exploiting diversity of distribution between target signals and jamming. Using the information entropy of the echo as the detection statistic, the binary jamming detector is designed to detect the DRFM jamming. Simulation results validate the feasibility and effectiveness of the proposed method. While the RSN is above 0 dB, the DRFM jamming detection probability is up to 0.9 for pulse compression waveforms, such as phased code and Linear Frequency Modulation(LFM).