To realize the automatic ranging function of packaging robot, this experiment proposed to apply sparse stereo vision to the packaging robot arm. To evaluate the accuracy of this algorithm, a robot arm REBot-V-6R which was equipped with stereo cameras was used to carry out the experiment to calculate the distance between the package pieces on the experimental table and the camera, and the accuracy of the algorithm was evaluated by the error between the value computed by sparse stereo and the measured value. Experimental results showed that the computing error was below 7% in a range of 600~1000 mm. In conclusion, the algorithm method of sparse stereo can be used in the ranging system of automatic packaging robot.