Abstract: This paper redefines software network and proposes a software network model based on the idea of a core inheritance tree. The internal node of the core inheritance tree plays an important role in functional and structural aspects of software through statistical analysis of eigenvalues. Between core number and degree exists a linear relationship in the internal node of the core inheritance tree. Between clustering coefficient and core number and degree exists an exponential distribution relationship in the internal node of the core inheritance tree. A hidden universal rule of large-scale complex software systems was discovered by researching the inheritance tree network model, thereby assisting the transition from traditional experience software engineering to calculation model software engineering.