Abstract：Research purposes： In recent years, the high-speed railway in China has developed rapidly, and its subgrade settlement has attracted more and more attention from the engineering community. But the research of subgrade settlement in seasonal frozen soil area is still in its initial stage. In this paper, first we study the characteristics of the high-speed railway subgrade in seasonal frozen area and the interaction between dynamic load and frozen-thaw cycles. Then we study the types, mechanism and development law of subgrade settlement. Finally we give a calculation model, method and an example.  Research conclusions： (1) Under the interaction between dynamic load and frozen-thaw cycle, subgrade settlement has different nature and mechanism in different cycle stages. (2) The subgrade settlement in seasonal frozen soil area includes compressibility settlement, pressure-dense settlement and thaw settlement. The maximum volume of settlement is produced during thawing of frozen soil. (3) The mechanism of settlement is mainly affected by the composition of soil, such as gas, unfrozen water and mineral particles, and under dynamic load the change of porosity is an important factor affecting the settlement. (4) The results of this paper can provide reference for subgrade design and maintenance in seasonal frozen soil area, and provide basis for the design and construction of high-speed railway subgrade settlement control.