To investigate the process of droplet impact on an orifice plate, a two-dimensional SPH model is established. An improved linked-list search algorithm with improvement of computational domain changing with fluid is described. By analyzing the numerical results with the experimental data, influences of viscosity, gravity, and internal pressure on the spreading of droplet over the orifice are studied. It is demonstrated that spreading will change to jet flow after the droplet reaches the orifice, and then the jet will pass it rapidly and in this rather short time the effect of gravity contributes very litte to the motion. However, viscosity can induce the jet to move in a curve into the orifice. Besides, with the internal pressure and inertial effect, the lower part of the jet will fluctuate regularly. The fluctuations make the jet repeat inflation and absorption to absorb the fluid from higher pressure area, resulting in Hole Suction phenomenon. Through analyzing the pressure of the vertical section of orifice edge, we find that internal pressure plays a significant role to the droplet which is absorbed into the orifice and finally leads to splashing. Numerical results are in good agreement with the experimental data.