Abstract: Based on the fundamental principle of telemetry receiving system, the CORDIC (COordinate Rotation Digital Computer) demodulation algorithm is comprehensively investigated. When the system input is an orthogonal IF (intermediate frequency) signal as well as its corresponding clock information, the system output is the instantaneous phase corresponding to the input transient signal. However, the anti-noise performance of the CORDIC demodulation is interfier to the coherent demodulation with the absence of channel delays. To this end, an improved CORDIC differential frequency discriminator demodulation algorithm in which the first-order difference is used in the digital domain for completing the signal frequency discrimination with the obtained instantaneous phase, is put forward to ensure the anti-noise performance of the signals in the channel without delays. Finally, the simulation results demonstrate the efficiency of the algorithm.