the root length is an important indicator to reflect the growth characteristics of the tree, but the root length is difficult to obtain through direct measurement, and the root as a sensitive organ of plants can indirectly reflect the growth state of plants, but it is also susceptible to external factors. the root length, as an important component of the root system, it can reflect the growth state of plant by using its own length change, and studies the influence of environmental factors on the root length, which helps to improve the yield of plants better. season, species composition, and soil condition are all factors that affect root growth. and the mutual effect between them cannot be ignored. past biological experiments have shown that the mixed biomass is greater than pure forest, and the seasonality affects the root length by affecting rainfall and temperature, but due to the lack of a single experiment, we can’t draw firm conclusions. therefore, our experiment uses the season and species composition as independent dependent variables through 3 groups of repetitions. our experiments are trying to verify two hypotheses that the fastest growing season of root is summer and root biomass in mixture stand is greater than pure forest. the tool that we used to measure root length in our experiment is minirhizotrons. we recorded three kinds of forest stand (conifer, deciduous and mixture) repeats three times and their five-month seasonal changes. we obtained data through rootsnap software analysis and verified our conjecture through statistical analysis this article reveal that the fastest root length increase is summer time and all species reach to the peak in august. the average of root length of all species in august is 96.11 cm and is 37.91 cm in june. this shows that the average root length increased by 1.5 times from june to august. however, there is no evidence to clear root length is longer in mixture compared to monocultures.