Abstract: Aiming at the roadbed frost damage of the seasonal frozen soil area around the Qinghai Lake section of Qinghai Tibet Railway, the typical distributed silty clay is collected focusing attention on the four factors: temperature, moisture, salinity, and compaction so as to conduct the indoor frost heave orthogonal test. The frost heave rates of subgrade soil under different temperatures have been tested, and the gray correlation degree analysis model is established to carry out the range analysis and variance analysis of orthogonal experiment. Then the influence of various factors on the frost heave is analyzed. The results show that the orthogonal test analysis and gray correlation analysis have the same law, and that the factors affecting the frost heaving are mainly temperature, salt content, water content, and compaction. The interaction between the factors is negligibly tiny, but the effect of temperature, salinity and water content on the frost heave is very significant. On the contrary, the interaction between compaction and factors has no significant effect on frost heave.