Abstract: Disclosed is a method for preparing 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) of formula (II), comprising the following steps: carrying out an alkylation reaction on cyclen in formula (I) and XCH2COOR in the presence of an acid-binding agent in water; adjusting a pH value to separate out a crude product of DOTA; and recrystallizing. The preparation method of the present invention is applicable to large-scale industrial production of DOTA, the whole process does not need to adopt an ion-exchange resin or low-temperature refrigeration mode for purification, and the purity and yield of the product are higher.