Based on matter wave and Sagnac effect, the angular velocity and acceleration in horizontal direction of the carrier can be measured by the horizontal atom interferometric gyroscope. The physical system is the key subsystem of a gyroscope, which provides the circumstances of ultrahigh vacuum with special magnetic distributions and optical paths for control and detection of atom states by lasers. To realize of atom interferometry and satisfy the requirements of high-precision measurement, the principles of atom interferometric gyroscope operation are analyzed, and the functional requirements and basic mechanical components are clarified. Based on the theoretical analysis, the key specifications including vacuum degrees and magnetic distributions of each functional area are proposed. Therefore, a physical system of atom interferometric gyroscope is constructed, the measurement results reveal that the vacuum held steady at 10 -8 Pa, and the diameter of cold atom cloud generating from this system is 6 mm, with the quantity of 8×10 9 and temperature of 12. 8 μK, which satisfies the requirement of the subsequent experiments.