Abstract: Air-core photonic crystal fiber is a new optical fiber used in fiber-optic gyroscope, which has better diamagnetic than traditional optical fiber. Magnetic-field sensitivity of the fiber is characterized by the Verdet constant of the fiber. In order to study the magnetic-field sensitivity of air-core photonic crystal fiber, Comsol software was used to simulate the Verdet constant of HC-1550-2 air-core photonic crystal fiber in this paper. At the same time, a dual-optical system including a Faraday Rotation Mirror (FRM) was chosen to measure the air-core photonic crystal fiber's Verdet constant. In the system, the FRM can eliminate the influence of the linear birefringence in the tested fiber on measurement. The measured results are in agreement with the simulation results. It can be seen from the results, Verdet constant of air-core photonic crystal fiber is nearly 1/100 of the traditional optical fiber, which verifies that air-core photonic crystal fiber has the advantages on decreasing the magnetic-field sensitivity.