Flat fan nozzles are widely used in industrial cleaning because of their large cleaning area provided by their uniform flat jet. Dynamic pressure and strike force are important parameters weighing cleaning efficiency, and reasonable matching nozzle diameter, pressure, and flow can make cleaning operations more efficient and save more energy. On the basis of established the threedimensional (3D) model of fan nozzle and the external flow field, using FLUENTs VOF twophase flow model to analyze and to compare the fan nozzles with different outlet diameters under different pressure, the strike forces and dynamic pressure were gotten. The results show that the nozzle diameter and pressure increase will both make strike force increase, but not the bigger of both of them, the higher rate of increase of strike force will be. With the same flat fan nozzles, jet pressure between 1~21 MPa, strike force will increase with increasing of pressure, but the magnitude of the increase will decrease. For example, the increase rate of jet strike force of 3 mmnozzle is 101% from 1MPa to 2 MPa of jet pressure, but from 20 MPa to 21 MPa, it is only 5%. Under the same jet pressure, fan nozzle outlet diameter between 1~3 mm, strike force will increase with increasing of outlet diameter, but the magnitude of the increase will decrease. For example, the increase rate of strike force under 2.5 MPa of jet pressure is 118% from 1 mm to 1.5 mm of increase, but from 2.5 mm to 3 mm of increase is only 42%.