The invention relates to a large-size special-shaped open caisson foundation construction method. The large-size special-shaped open caisson foundation construction method comprises the steps that foundation pit surveying and setting out are conducted, a site is leveled, an open caisson cushion layer is manufactured, and blade foot manufacturing is conducted; then a first open caisson section is prefabricated, an inner side scaffold and an outer side scaffold are erected on the inner side and the outer side of the well wall correspondingly, a formwork is mounted, and concrete is poured; afterthe first open caisson section reaches the design strength, in-well soil taking sinking is conducted; then a second open caisson section is prefabricated, an outer side scaffold is erected on the outer side of the well wall, an operation platform is erected at the top of the first open caisson section, and an inner side scaffold is erected on the operation platform; and the formwork is mounted, concrete is poured, after the second open caisson section is completed, in-well soil taking sinking is conducted, manufacturing sinking of the next open caisson section is conducted according to a manufacturing method of the second open caisson section, and finally open caisson bottom sealing is conducted. According to the open caisson construction method, the scaffold erecting, material using and erecting time can be saved.