A fire fighting cannon is fire-fighting equipment developed for fighting against forest fires; it is considered the tree crown fire and the inaccessible areas which are dangerous for man to get close as extinguishing object. The forest fire fighting cannon is launched by pneumatic method; the timing device within the extinguishing shell will be triggered after launching. After the free-flying and the parachute deceleration phase, the shell will detonate while the temperature in the fire field detected by the temperature sensor arrives at the setting value. The control system of the fire extinguishing cannon was designed firstly, the fly ballistic trajectories were analyzed and calculated, which are involved with the interior ballistic in the process of launching, the exterior ballistics analysis in the state of free-flying with non-parachute and the process of deceleration flight with parachute open. The ballistic calculation provides control with the necessary parameters.