Abstract: The experiment of transplanting container seedlings of Manglietia yuyuanensis with different container sizes was carried out. The effects of container size on seedling growth dynamics and growth rhythm were analyzed by using the method of fixed plant observation and fitting seedling height and ground diameter growth with Logistic equation, and path analysis was used to reveal the mechanism of seedling growth process and rhythm. The results showed that the effect of container sizes on promoting growth appeared with the time after transplantation, and it is a dynamic process. Container sizes significantly affected the height and ground diameter growth rhythms of M. yuyuanensis seedlings, such as the linear beginning days, the final days, linear growth rate, maximum linear growth rate and total linear growth; container sizes significantly affected the height linear growth duration. Linear growth duration and linear growth rate had significant promotion effects on seedling height and ground diameter growth; linear growth rate was the dominant growth rhythm factor affecting seedling growth. The mechanism of affecting seedling height and ground diameter growth by container sizes is mainly realized by changing linear growth rate.