Growth measuring for plant is an important work both in agriculture and botany. Computer vision provides a convenient non-contact way for measurements in many fields. In this paper, a growth measuring approach for maize based on computer vision is presented. Firstly, a computer vision system for maize in field consisting of binocular camera on a path beam is constructed, and doubles of maize images are captured. Under the definition of average growth velocity of maize, we measure the growth of given maize plant by image processing and relevant calculations. Part of experimental results are given and discussed. Results and analysis show that the presented method is practicable for maize growth measuring in assigned time period. Finally, some limitations are pointed and more future works are addressed in computer vision-based measurement for plants.