A new method for measuring of the geomagnetic field vector and magnetometer option for its implementation was proposed as a solution to the problems in the sphere of the geomagnetic fields' measurements during geophysical and cosmic investigations. Under consideration is a magnetometer option, which uses one flux-gate sensor, as a basic functional element, oriented on measurement of three orthogonal components of a weak magnetic field, rigidly connected with the platform axes, on which the magnetometer is installed. The vector parameters of the investigated field are defined by means of the magnetometer at the previously known orientation of the platform axes. Application of the additional effect of the useful signals modulation, which arises during rotation of the flux-gate sensor in the residual field and during its biasing by the test alternating magnetic field, allows us to minimize all the measurement errors of the field components: graduation errors and sensibility variations (multiplicative error); zero shift and fluctuation (additional error). In the work a new test measurement algorithm is substantiated; an option of magnetometer structural block-diagram is considered; peculiarities of the measuring procedures and magnetometer functioning modes are analyzed. The proposed option of the magnetometer in combination with separate types offlux-gate sensors has high reliability, resistance to interferences, insignificant power consumption, relatively small weight and dimensions. The use of such an option of magnetometer as a precision null-indicator will allow us to measure accurately the geomagnetic field components, to carry out the works, connected with different geophysical investigations; with determination of the magnetic deviation, created by different movable objects. With its sufficient sensitivity and high precision of transformation, as well as a sharp directivity graph, the magnetometer option under consideration may be used also in the tracking systems, allowing orientation of different objects on the geomagnetic field.