The performance of the flat jet with an inclination angle was investigated by a water model. A mathematical model for the shrinkage and the trajectory of the flat jet with an inclination angle was derived theoretically and verified by experimental data of the water model. The experimental results indicate that the inclination angle (α) has no influence on the shrinkage of the flat jet, the shrinkage of the flat jet along the width direction decreases with the increasing of the initial velocity at the exit (u0) and the initial thickness of the flat jet (t0). Enough bigger initial exit velocity (u0) and initial thickness can suppress the shrinkage of the flat jet along the width direction and keep the flat jet stabilized. In addition, the trajectory of the flat jet with an inclination angle is parabolic and must be taking into consideration when to determine the striking distance. The performance of the flat jet with an inclination angle was investigated by a water model. A mathematical model for the shrinkage and the trajectory of the flat jet with an inclination angle was derived theoretically and verified by experimental data of the water model. indicate that the inclination angle (α) has no influence on the shrinkage of the flat jet, the shrinkage of the flat jet along the width direction decreases with the increasing of the initial thickness of the exit (u0) and the initial thickness of the flat jet (t0). Enough bigger initial exit velocity (u0) and initial thickness can suppress the shrinkage of the flat jet along the width direction and keep the flat jet stabilized. In addition, the trajectory of the flat jet with an inclination angle is parabolic and must be taking into consideration when to determine the striking distance.