In combination with the similitude principle of emulate structural model test, according to the theory for calculating crack width and the statistical analysis of test data, the methods were established for calculating the similitude ratios of average crack spacing and maximum crack width of reinforced concrete beams respectively. The applicability was studied by comparative tests from the large reinforced concrete beams to the emulate model test beams, including two groups of two  dimensional similarity beams and one group of three-dimensional similarity beams. It is realized that the crack distribution and its width of model beams feed back to prototype beams, which can be used as a reference for the design of abnormal emulate model test.