The ultrasonic parameters,such as amplitude and wave shape and ultrasonic velocity were monitored during explosive cast process with the heat preservation and natural cooling by using ultrasonic transmission test. The results show that the ultrasonic amplitude at the bottom position of explosive is obviously greater than that at the middle and top positions,indicating the quality of cast explosive at bottom is the best. The ultrasonic amplitude of explosive with heat preservation is larger than that with the natural cooling at the same position,indicating that heat preservation technique is effective to control cast quality.