In this study, two oil-water systems of oleic acid-water and chloroform-water are used as samples. Ultrasound is sequentially irradiated using five ultrasonic transducers at 20 kHz, 0.5 MHz, 1.6 MHz, 2.4 MHz and 4.8 MHz to produce emulsion. The distribution of droplet diameter is measured. The effects of ultrasonic frequency and oil kind on the emulsion characteristics are experimentally examined. For the oleic acid-water system, the droplet diameter decreases and the stability of emulsion increases as the step number and the frequency of tandem acoustic emulsification increase. The emulsion formed by tandem acoustic emulsification at 4.8 MHz is still stable after 7 months. The stability of emulsion decreases with increasing oil volume fraction. For a chloroform-water system, the diameter and polydispersity of droplet become drastically small by tandem acoustic emulsification. Compared with the oleic acid-water system, the stability of emulsion was low.