Based on the feature that Helmholtz coils can produce a uniform magnetic field, we made triaxial Helmholtz coils to generate magnetic fields with three orthogonal directions for simulating the geomagnetic field intensity by changing the importing electrical current of the three coils.This device could offer geomagnetic field environment for the hardware-in-the-loop simulation of geomagnetic navigation system.A lot of experiments were made to find whether this device is suitable for the need of simulation.These experiments included the tests on repeatability and linearity, and on response speed, uniformity and stability.The input/output model of the device was also established.These experiments proved that the indexes of the device can satisfy the needs of the laboratory.