The phenomena of droplet impact on an inclined solid surface covered with a pre-existing liquid film are observed using high speed camera at 10000 frames per second. The processes of droplet spreading, liquid sheet formation, splashing and droplet oscillation are observed and analyzed. From the results the relationship between spreading velocity and time is discussed quantitatively. Besides, the effects of impact velocity and impact angle on front and back spreading factors and initiatory spreading velocity are also revealed. At the impact angles ranging from 28.0° to 74.7°, it is found that with the decrease of impact angle, the deformation degree of the droplet oscillation on the film surface increases. The results also indicate that the front spreading factor can increases by increasing impact velocity or by reducing the impact angle, whereas the back spreading factor increases with impact angle increasing. The impact velocity almost has no influence on it. The initial spreading velocity can increase by increasing the impact velocity and the impact angle.