Based on the flexural static loading test of six concrete beams,the crack distribution and development of CFRP - PCPs ( carbon fiber reinforced plastics prestressed concrete prisms) composites reinforced concrete beams under service load were researched. Considering the influence of CFRP - PCPs composites reinforcement,the calculation methods of maximum crack width and mean crack spacing of concrete beams with CFRP - PCPs composites reinforcement in current Chinese design code for concrete structures were modified. Whose results were compared with experimental results,showing a better agreement between test values and the calculated values given by the modified formulas.