The invention relates to a calculation method for constructing a gravitational gradient field of a complex body. The method is technically characterized by comprising the following steps of enabling the complex body to be equivalent to a charged insulator, enabling a gravitational field to be equivalent to an electric field, and performing mesh division on a model; calculating a gravitational field between two objects, enabling the density to be equivalent to charge density of a charged body, and multiplying the density by a conversion coefficient to obtain a gravitational field around the complex body; and performing derivation on gravitational components along three coordinate axes in a rectangular coordinate system, regarding the gravitational components as deformation of the objects in three coordinate directions, and calculating out strain generated under the deformation, wherein linear strain corresponds to a linear gravitational gradient, and shear strain corresponds to a cross gravitational gradient. The method realizes calculation of the gravitational gradient around any three-dimensional mass body, is suitable for directive calculation of a self gradient of a gravity gradiometer, a basic gradient of a lab and artificial gradient excitation generated by an experiment apparatus, and lays a solid foundation for gravity gradient inversion and geological interpretation.