Abstract: The urban sewage system and drainage system belongs to different departments in China,which adopt different design codes during designing processes and thus lack coordination in design combinations. In order to avoid potential waterlogging risk and over-investment,this research takes Zhongshan and Zhuhai as study areas and develops a design combination selection method of urban sewage and drainage systems based on Copula Theory and Most-Likely Estimation（MLE）Method. The MLE design combinations with different Kendall’s return periods are obtained thereafter. Results show that joint distributions between precipitation series with different kinds of duration can be effectively constructed with good fitting effects of Copula theoretical probabilities and empirical probabilities. The MLE design combinations obtained in this research revealed that the raw design scale of sewage system is underestimated while the design scale of drainage system is overestimated for the downtown area of Zhongshan City,which provide scientific references for adjusting the design scheme of sewage and drainage systems.