Abstract: Laser thrusters with single nozzle of parabolic or conic profile fail to constrict the high-pressured flow efficiently, resulting in poor propulsion performance. Under air-breathing mode and different single-pulse laser energy, the laser thruster with elongate cylindrical nozzle which features a parabolic nozzle tailed by a cylindrical nozzle is studied numerically for different shape parameters by building physical computation model. Readily, its impulse coupling coefficient is tested to be more than 600 N/MW with a good accordance with the foreign experiments. Meanwhile, the results show that, the impulse coupling coefficient increases along with cylindrical nozzle length and approaches a constant value, and the proposed cylindrical nozzle saturation length increases linearly with laser