The lateral earth pressure coefficient at rest, K0, is an important parameter in geotechnical engineering. There have been many studies for unfrozen soils; however, this is not the case for frozen soils, which impedes reasonable calculation concerning cold regions engineering. This paper introduces a novel triaxial apparatus for frozen soils with reference to that for unfrozen soils. The device is capable of performing experiments on frozen soil samples with K0 status under precisely controlled negative temperature. Two soils along the Qinghai-Tibetan highway are taken as study objects. K0 experiments are carried out with the apparatus and K0 is obtained under different testing conditions. It is found that temperature is a dominant factor in influencing K0 of frozen soils, while stress state and soil type should also be taken into account.