The invention discloses a method for pre-estimating an equivalent thermal conductivity of an unidirectional fiber toughening composite material based on gap defect identification, wherein the method mainly comprises the following steps: processing a material micro electron microscope image by using a picture identification technology, and identifying material internal structure characteristics and gap defects; according to a fiber volume fraction ratio stability criterion, applying a geometric reconstruction technology, establishing a representative element geometric topology model, and simultaneously determining the gap defects; through a method of adding a thermal contact resistance at a representative element internal interface, introducing influence of the gap defects; and simulating to obtain the equivalent thermal conductivity by using an finite element method. According to the method, the representative element considering the gap defects is established based on image identification of an actual micro structure, and calculation of the equivalent thermal conductivity is carried out, an influence rule of gap defect position, number, thickness and other characteristic parameters on the equivalent thermal conductivity is analyzed, and a technical reference is provided for high precision pre-estimation of the thermal conductivity of same-type composite materials.