To study mechanical properties of frozen soil under complex stress path, a novel frozen soil testing system-Frozen Hollow Cylinder Apparatus-300(FHCA-300) was developed by State Key Laboratory of Frozen Soils Engineering and the GCTS company in America. By independently controlling inner, outer confine pressure, axial load and torque, this apparatus can change the magnitude and direction of three principal stresses to accurately simulate the stress-strain behavior of frozen soil under complex stress path including the principal stress rotation and multriaxial stress induced by traffic or seismic. This paper introduced the components of FHCA-300, the selection process of sensors, the frequency of dynamic load and the concrete experimental types in details. The design principle of the temperature control system was concretely presented, and the temperature control ability was verified as well. The results show that the system can meet the desired temperature control requirements. For investigating the apparatus' performance of realizing the complex stress path including principal stress rotation, static principal stress axis rotation and cyclic rotation tests were designed, preliminary test results show that the instrument can accurately reproduce the frozen soil mechanical and deformation behaviors in complex stress path condition. It provides technical means for systematical researches on the strength, deformation characteristics and constitutive relation of frozen soil under complex stress condition.