Laser propulsion is one of the promising solutions to the cost morass of chemical rockets. Laser supported detonation (LSD) is an important phenomenon formed in laser radiation, which would significantly enhance the specific impulse with an appropriate laser intensity. When the intensity is high enough, the total number of particles is evidently different through the LSD wave, and the dissociation and ionization energy must be considered. Taking account of these impacts in the conservations of mass, momentum and energy, a modified analysis of LSD is presented and the flow state behind the LSD wave is obtained. Calculated results are compared with the classical Raizer's model and experimental data. Furthermore, performances of laser propulsion are evaluated based on a 1-D assumption. The study concentrates on a better understanding of LSD and laser propulsion.