Temporary cofferdam is needed to stop water and dewatering during the construction of the outlet cofferdam in the D section of the second phase extension project of Guangxi Qinzhou power plant,so as to obtain the dry construction conditions.After scheme comparison and optimization,scientific calculation and reasonable demonstration,the combined structure of filling sand bag,jet grouting piles,steel sheet pile,cast-in-place pile,brick water-stop wall,water-stop ring beam and water-stop clay wall is adopted.Based on the characteristics of different water-stopping structures,the structures of cofferdams in water area and land area under different environmental conditions are optimized and designed reasonably,which effectively solved the construction difficulties such as small local space and large head difference,and achieved good engineering results.This method has certain reference value in the design optimization and selection of similar projects.