An additive machining formation method suitable for complicated parts and molds. The method comprises the following steps: building CAD geometric models of parts or molds; extracting an STL model, and dividing the STL model into multiple layers according to a preset layering thickness; respectively extracting inner and outer profile points of the multiple layers to form inner and outer profile trajectories; generating, based on the inner and outer profile trajectories, numerical control instructions corresponding to the machining of each of the layers; selecting plates, the thicknesses of which are layering thicknesses, and taking same as machining objects of each of the layers; cutting each layer of plate by means of a cutting device according to the numerical control instructions corresponding to the machining of each of the layers; stacking and accumulating each of the layers in sequence to obtain primary blanks or primary blank blocks; during stacking and accumulation, carrying out precise positioning once every time one layer is accumulated; and then, carrying out vacuum dispersion connection with regard to the primary blanks, or first carrying out vacuum dispersion connection, then accumulation and finally vacuum dispersion connection with regard to the primary blank blocks. The method involves high forming efficiency, high forming precision, low material costs and good forming stability.