Frequent extreme cold events in recent years have brought serious threats to outdoor workers and rescuers. Changes in ambient temperature are associated with altered cardiac autonomic function. The study aims to investigate heart rate variability(HRV) and its relationship to other physiological parameters under extreme cold exposures. 12 males underwent a 30-minute preconditioning phase in a neutral environment followed by a 30-minute cold exposure(-5 degrees C, -10 degrees C, -15 degrees C, and -20 degrees C). Time-domain indexes(meanRR, SDNN, RMSSD, and pNN50), frequency domain indexes(Log(HF), Log(LF), and low frequency/high frequency(LF/HF)), parasympathetic nervous system(PNS), and sympathetic nervous system(SNS) were analyzed. Results showed all HRV indexes of four cold exposures were significant. The decrease in temperature was accompanied by progressive PNS activation with SNS retraction. SDNN was the most sensitive HRV index and had good linear relationships with blood pressure, pulse, and hand temperature. The results are significant for formulating safety protection strategies for workers in extremely cold environments.