Getting accurate geomagnetic field measurements on the route of the vehicle is the precondition for geomagnetic navigation. The interferential magnetic field of the vehicle would distort the outputs of the magnetometer and influence the matching precision, so it must be compensated. Based on the analysis of the characteristics of the vehicle magnetic field, a method to compensate the geomagnetic magnitude, using vector measurements, is presented. A formulation was derived according to the measurement model of vectorial magnetometer, a nonlinear evaluation method was adopted to evaluate the vehicle interferential fields parameters, and then the evaluated results were used to compensate the real- time measurements. A simulation was conducted to test the effect of the method and an experiment was performed to validate its practicability. The results show that after compensating with the presented method, the measurement error of geomagnetic field magnitude is less than 20nT, indicating that the method has high compensating precision, good convenience in use, and can compensate the interferential magnetic field of the navigation vehicle effectively.