Abstract: In order to analyze the growth rhythm of corn root, experimental filed located in the large root monitoring system of Gu Cheng agrometeorological station was chosen in this research to study the application of minirhizotron in monitoring of the growth dynamics of crop root. Minirhizotron observation method was applied to monitor the growth rhythm of corn root, and reference standard used in this research was the square whole specimens method. MATLAB image processing technology and modern statistical method were applied to analyze the experimental data. Results showed that corn root length density decreased with the soil depth increasing observed through the two methods. The results of the two methods were significant correlation with the correlation coefficient above 0.83 at 95% confidence level. The regression equation of root established by the observational data could reflect the growth rhythm of corn root. It further shows that the minirhizotron method is a less destructive and accurate method to monitor the growth of plant roots dynamic change in soil. The minirhizotron technique has a good application value on the monitor of corn root growth.