Aiming at the large trigger delay of digital oscilloscope, a novel multi-frequency measurement method is presented. By using the period of sinusoidal as standard, the large trigger delay is divided into two parts; one part just consists of many periods of sine wave, the other part includes the partial period of sine wave. The partial period part can be measured through phase difference method, and to the integer periods part, by using the nominal trigger delay divide the stimulation frequency, one can calculate the number of periods. Finally, through compounding the two parts, the large trigger delay is gotten. The correctness and feasibility are proved by some experiments on digital oscilloscope, and the method can be used in the calibration of large trigger delay of digital oscilloscopes.