Under the concentrated loads, the crack evolutions of reinforced concrete experimental beams (RCEB) with three different aggregate sizes are studied. Using fractal theory, the generation, development and distribution of the cracks on the RCEB are analyzed. The results show that the cracks on the RCEB have fractal characteristics obviously. By studying the fractal dimension of the cracks, the aggregate sizes have significant effect to the cracks on the RCEB. The relationships of the fractal dimensions of the crack evolution in loading processing and loads meet the power function laws. The researching results of this paper provide a new theoretical basis for selecting the appropriate aggregate size to improve the strength of reinforced concrete beams.