Abstract: Analyzing the interaction mechanism of laser with target and vaporized target material, a one-dimensional bulk absorption model to simulate the solid target ablated directly by the laser beam is presented, numerical calculation of impulse acting on the target in vacuum with different laser parameters is performed with fluid dynamics theory and 1D Lagrange difference scheme. The calculated values of the impulse coupling coefficient are in good agreement with the experimental results and Phipps’s empirical value. From the calculated results, the impulse coupling coefficient decreases with the increment of laser intensity when the laser pulse generates a plasma.