In this paper are analyzed the characteristics of the single photon detector (SPD) with using coaxial cables as reflection lines to cancel transient spikes noises, particularly,the characteristics of variations in bias voltage of the avalanche photodiode (APD) and output signal. Based on the theoretical analyses,the principle of the timing relation between single photon pulses and the two gate pluses is discussed. Also, the condition and the effect of transient spikes cancellation are achieved. And the minimal detecting period is obtained. Finally,we conduct some experiments to verify our theory. In our experiment,the noise rejection ratio is 25.1dB. The results accord with our theory satisfactorily. Our results will be helpful in designing and optimizing single photon detectors.