The photoelectric gate commonly used in ordinary physics experiments can only count the number of light blocking and total time．Through the audio card，the photoelectric gate data can be collected and every time of light blocking can be obtained，which provides the possibility to study the vibration law of the large damping pendulum．The first-order difference is made to the voltage data sampled，and the positions of the
positive and negative pulses corresponding to the rising edge and falling edge of the original sample signal，respectively，and which is the moment when the photoelectric gate is blocked at the beginning and end．The calculated period of the pendulum decreases with time，and the results of the long-time large damping pendulum experiment are in good agreement with the results of the perturbation method． The damping coefficient of the air is estimated according to the light blocking time of the photogate，which is consistent with the results in related literatures．The research results provide the feasibility for the study of complex vibration
phenomena by using ordinary photogate．