Abstract: There exists a direct relationship between the weld pool oscillation frequency and volume of weld pool. But the detection of oscillation frequency in on-time travelling condition is difficult. In order to detect the oscillation frequency in real-time, a new laser photoelectric conversion method was proposed. Several experiments with travelling welding condition were conducted and the frequency was extracted by Fast Fourier Transform. The results show that image laser-vision method has a strong anti-disturbing ability and high signal-to-noise while the defect of image process is complex and real-time detection becomes worse. The laser photoelectric conversion method with high sampling rate, high processing speed and simple device can completely satisfy the requirement of measuring the oscillation frequency of weld pool in practical welding process.