The invention relates to the field of constructional engineering, in particular to a cofferdam construction method. The cofferdam construction method comprises the following steps of: surveying and setting out, performing diversion channel excavation and construction, performing sandbag side slope protection, performing steel plate pile checking, positioning and setting out, mounting a guide truss, inserting a steel plate pile, mounting an inductor, and performing water drawing, desilting and backfilling-leveling in a cofferdam. Compared with existing cofferdam construction, the cofferdam construction method has the advantages of being high in efficiency, capable of efficiently monitoring construction details, effectively shortening the construction period and improving construction quality, and can timely notice the maintenance unit of the quality problem which appears in a building construction process.