Laser sustained plasma (LSP) propulsion mechanism is the key to laser propulsion technology. On the basis of the average atom (ion) model (AAM) and the collision radiation model (CRM), the interactive process between laser and plasma is simulated by coupling method to obtain some characteristic parameters. The experimental results of laser shooting carbon target prove the exactness of simulated results, and show that laser dipulse shooting carbon target can produce more impulse coupling coefficients by 50% at maximum than that by single pulse, which is favored to laser propulsion. This meaningful work will provide reference for further investigation on laser sustained plasma propulsion.