In view of the divergence in the size effect analysis of concrete nominal strength between the size effect law and boundary effect model of concrete, a novel size effect model based on a power law and equivalent elastic crack method was proposed. The influence of the specimen size, initial crack length and fracture process zone on the nominal strength of concrete was taken into account in the proposed model simultaneously. The influence factors of size effect law and boundary effect model were included in the proposed model, the few empirical parameters of this model were convenient to determine. The proposed model was verified through the experimental data and research data in the existing literature. The results show that the proposed model can properly describe and predict the quasi brittle fracture behavior of concrete material, the limit of size or geometry of the specimens will vanish.