Based on the MFPA2D software system and test method of the wedge splitting fracture in the Lab., a numerical model was established. The numerical experiments on wedge splitting fracture with plain concrete and SFRC (steel fiber reinforced concrete) were carried on. The calculation results about plain concrete with different dimensions and ligament length proved the numerical model is effectively on numerical calculation, and have a good agreement with the results of the test results. Then, the process of crack initiation, propagation of SFRC specimens with different dimensions and fitting formula about size effect were given. The results indicated that the size effect existed in the splitting fracture energy of SFRC.