Abstract: In order to study the growth rhythm of maize root, a large root monitoring system was used in an experimental filed to analyze maize ('NO. 46 Tunyu') root. The minirhizotron observation method and the quadrate monolith method were used to monitor the main parameters such as maize root length, root length density and root length ratio at milky and maturity stage. Meanwhile, underground glass windows were used to measure root length and width. The results showed that root length density ratios measured by the minirhizotron observation method and the quadrate monolith method were consistent with the increase in soil depth at milky and maturity stage, with correlation coefficients of 0.987 and 0.717, respectively. Root length density ratios estimated by the two methods were highest in 0 20 cm soil layers. The 0 60 cm soil layers were the primary growth zone of fine roots, with average net root length density 4 times that in the 70 220 cm soil layer measured by the quadrate monolith method. Root length densities from the two methods were not significantly different, with a correlation coefficient of 0.830. The horizontal width of roots in the upper soil layer became narrower with increasing vertical depth from milky stage to maturity stage. This suggested that roots still grew during late developmental stage. Differences were noted in root depth between the quadrate monolith method and the underground glass window method, probably due to inconsistent environmental conditions.