The invention belongs to the field of engineering magnetic field modeling, and provides a method for measuring the magnetic field noise coefficients of an underwater vehicle based on a small signal method, and the method comprises: an UUV (Unmanned Underwater Vehicle) background magnetic field model is built; a magnetic field vector of UUV measuring environment is measured in advance; the placement direction of an UUV is changed, and corresponding Hx1, Hx2, Hx3 and Hx4 are measured through the changes of large-angle attitudes; the other conditions are not changed, a vertical direction magneticfield is applied to the UUV, and the rolling angle and the pitching angle are kept to be zero, the pointing orientation of the UUV is changed horizontally, and Hx5, Hx6, Hx7 and Hx8 are respectivelymeasured through the changes of the large-angle attitudes; a constant magnetic field, an induction magnetic field coefficient and a geomagnetic field are calculated, the above steps are repeated, andother parameters of the UUV magnetic field are calculated. According to the method, the correlation between the noise coefficients of the magnetic field and the multicollinearity of the model are effectively reduced, the influence on the energy spectrum of useful signals in the magnetic field is avoided, and the subsequent detection and identification of weak useful signals are facilitated.