A parameter of crack resistance Φ is proposed as an index to assess crack resistance of RCC comprehensively. The higher the value of Φis, the better crack resistance of RCC becomes, and it was tested and verified by indoor experiment. Meanwhile, time effect of the parameter is also studied deeply, and the characteristic of development of crack resistance is presented. Ф changes with the passage of the time. Its value decreases before 14 days, but increases after 14 days, and it is minimal at the age of 14 days, which means that crack probably exists. Finally, We improve crack resistance of RCC by improving transition zone and toughness of binding materials, optimizing aggregate and adding admixtures etc.