Abstract: By ultrasonic tachymeter, home-made hammer impact device and ZDKT-1 transient magnetic testing system, the changes of ultrasonic velocity through coal briquette and the characteristic of transient electromagnetic signal in the process of coal impact damage were researched. The coal briquettes were with different particle sizes and different forming pressure respectively. The results show that: the coal briquette strength is influenced by the coal particle size and forming pressure. Ultrasonic velocity increases along with briquette forming pressure which leads to more compact and strength of briquette; transient electromagnetic signal of coal briquette in the process of coal impact damage has a characteristic of omnidirectional and pulse type; with the same particle size and impact load, the more coal briquette strength it is, the more energy of transient electromagnetic signal releases in the process of coal impact damage.