Ping-pong ball detection plays an important role in the vision system of ping-pong playing robots. In the paper, we present a fast ball detection method for ping-pong playing robot. A reasonable searching region is proposed based on the ping-pong table and the prediction of the ball's current position. Five key points are used to detect the ball in our method to meet the ping-pong ball's high speed. Because we use points to the ping-pong ball instead of the ball's region, the process of the detection can be finished during one scanning, which greatly increases the detecting speed. Experimental results verify the feasibility and the efficiency of our method.