Abstract: Previous studies indicated that the size effect has significant influence on the shear capacity of deep flexural members with lightweight aggregate concrete, but it has not been reasonably considered in most existing design codes or typical shear models. This paper proposed a shear model by combining the energy-balance theory in crack band with the strut-and-tie model. Then it was simplified by quantifying the contribution of diagonal strut and shear reinforcement according to a large set of data on normal concrete specimens from the literature. The accuracy of the proposed shear model was observed by comparing it with the computational methods in most existing design codes. Furthermore, this paper modified the proposed model based on the difference in shear fracture mechanics between normal weight and lightweight aggregate concrete. Combined with the eight completed experimental study in this paper, a shear model for lightweight aggregate concrete deep flexural members considering the size effect was presented and verified. It is shown that the predicted results by the new model based on energy-balance theory were in better agreement with the test results than those determined from others current design codes or the Tan-Cheng model. The proposed model with definite shear transmission mechanism and reasonably considered size effect can accurately evaluate the shear capacity of deep flexural members with lightweight aggregate concrete.