Single-well refracturing treatment can be divided into two forms, including the formation of a new diverting refracture at the wellbore and the formation of an expanded refracture based on the initial fracture. It is very important to evaluate the productivity of wells under different fracture systems after refracturing for optimizing the refracturing construction scheme. In this study, complex fracture systems produced by refracturing treatment are taken as the research object. The numerical model is established by using the embedded discrete fracture method. The production law of reoriented and expanded fracture systems after refracturing is studied, and the influence of different fracture systems on well productivity is clarified. By comparing the productivity of reoriented and expanded refracture systems, it is found that changing the reservoir or fracture parameters respectively will affect the productivity of refractured wells in different degrees, and the effect on expanded refracture system is always greater than that on reoriented refracture system. Considering the permeability anisotropy of the reservoir, the higher the matrix permeability orthogonal to the initial fracture extension direction, the better the effect of production increase after refracturing, and the more significant the cumulative production increase of the expanded refracture system. The more the refracture tends to be orthogonal to the initial fracture, the more obvious the increase in production after refracturing, and the increase in the production rate of expanded refracture system is higher than that of reoriented refracture system. Both refracture permeability and refracture length are positively correlated with refractured well production increase, and the cumulative production increase trend of expanded refracture system is more significant. As a result, the expanded refracture system can be more effective in increasing refractured well capacity. The results of this paper have guiding significance for understanding the mechanism of refracturing and field application.