Abstract: In May 2017, 3-year container Pinus sylvestris var. mongolica seedlings were transplanted in root-guiding tubes with length of 20 cm, 40 cm, 60 cm, 80 cm and 100 cm, and observation and determination was made on root growth out of tube. The results showed that the vertical root growth of tested seedlings had characteristic of slow-fast-slow. The slowest was from transplantation to 20 cm, the fastest was from 20 cm to 40 cm, and then the growth rate gradually decreased. Taking root vertical length as the dependent variable and growth days as the variable, the Logistic model for root vertical growth of P. sylvestris var. mongolica was established, with the determinant coefficient was 0.958 2, indicating that the model fit well. Based on this model, the growth of vertical root was divided into four stages: the gradual growth period of 0-25 days, the rapid growth period of 26-46 days, the slow growth period of 47-67 days and the gradual stop period of 68 days later.