A method for eliminating the weak optical background is presented in the pulse laser transmitting using the acousto-optical delay effect. The background photons with the same optical frequency of the pulsed laser can be suppressed effectively by using two tandem acousto-optic modulators working as optical switches. The signal to noise improvement ratio is up to 13 dB. Here, the first acousto-optic modulator is used to separate the pulse signal and the background photons in time domain. The second one is used to notch the separate background photons. This method could be applied in the range of precision measurement and information processing for pulse light sensitive detection.