There is no unified method in the design standards of municipal sewerage and waterlogging drainage at present. In order to guarantee that the designed return period rainstorm can be discharged successfully, it's very essential to construct the cohesion between the two.Using long sequence of rainfall data in Guangzhou,the paper constructed the cohesion of return period in short and long duration.It can be found that the difference of confluence duration is the main reason for making a larger difference in their return period.Through analyzing the cohesion relationship of rainstorm peak of rainstorm line between municipal sewerage and waterlogging drainage, the results show that the return period of rainstorm peak of municipal sewerage to waterlogging drainage is about 5 times, which mains that return period of municipal sewerage of 1 year frequency corresponds to waterlogging drainage of 5 years frequency.