Abstract: Objective The derivative of magnetic vector components plays an important role in the magnetic targetinterpretation process.A boundary effect problem is found in the computation of higher order deriva-tives of magnetic potential using the common methods such as the fast Fourier transform algorithm inactual applications.The paper presents a solution based on aπ/2phase-shifted cosine transform andits time-differentiation.Unified formulas for calculating the derivatives of magnetic vector componentswere deduced,and then applied to the directional analytic signals method.An analysis and comparisonof magnetic field data between the rectangular prism source model and cosine transform method showthat the influence of boundary effect can be avoided.The proposed method not only has higher preci-sion and stability,but also doesnot require additional data and algorithm complexity for extendingedge and filter processing.