Abstract: Fast and accurate methods for determining root growth in situ are important tools. In the present study, a rhizotron tube method was trialed as a means to more conveniently observe the dynamic development of roots under conditions similar to those encountered in the field. Crops were planted in transparent tubes covered with photomask to ensure a dark environment in the tube. This method can also be used in field studies of deep root development in crops by changing the length and diameter of the tube. Combined with root scan technology, we investigated the dynamics of root growth in oilseed rape and winter wheat at the seedling period from 16 days after germination. The results showed that winter wheat had a larger root and shoot dry weight than oilseed rape at both 7 days and 16 days. For winter wheat and oilseed rape, the root to shoot ratios at 16 days after germination were 0.513 and 0.372 respectively; the ratios of root length to total root length in the top soil layer (0-16 cm) were 62.60% and 67.76% respectively. The total surface, total volume and number of first class lateral roots of the two crops both had larger percentages in the top soil layer, indicating that most of the roots were distributed in the top 16 cm soil layer at 16 days. At 7 days after germination, the total length, total surface, total volume and number of first class lateral roots in winter wheat were higher than those in oilseed rape, while there were no differences between the two crops for the total length and total surface of roots at 16 days, suggesting that the root growth of oilseed rape was slow in the beginning but fast thereafter. The average root diameter in top soil was smaller than that in the deep soil layer, and the average root diameter of oilseed rape was smaller than that of winter wheat, which was typically between 0-0.50 mm. In terms of root growth, there were more and more thinner lateral roots, meaning that average root diameter became smaller. At 16 days after germination, the root elongation rate of winter wheat was 1.83 cm/d, larger than that of oilseed rape (1.51 cm/d). In conclusion, the root growth of winter wheat at the seeding stage was faster than that of oilseed rape, and the root of oilseed rape grew slowly at the beginning but faster thereafter. The rhizotron tube method introduced in this research is recommended as an effective method for root study in situ.