Ultrasonic amplitude-variation bar type reactor has been employed to probe the liaohe heavy oil ultrasonic cracking viscosity reduction. The effects on reaction temperature, processing time and ultrasonic power, to the viscosity reduction ratio, were investigated. In the experiment, ultrasonic processing parameter were optimized, the energy consuming of ultrasonic processing and viscosity reduction cracking was calculated and compared. the viscosity reduction effect (1 kg heavy oil in Liaohe)reached the optimum under the condition of high pressure(experimental pressure 8 MPa), ultrasonic power 1.5 kW, processing temperature 300 ℃ and processing time 20 min, where the viscosity reduction ratio of 1 kg heavy oil was 47.69%; the most important factor of viscosity reduction ratio was ultrasonic power; ultrasonic processing time and temperature took second place. Compared to viscosity reduction cracking technology, ultrasonic processing had the advantage of low power consuming, during processing the same samples, which provided effective method to reduce the viscosity of heavy oil with low energy consuming and high efficiency.