The invention relates to a method for BIM assisted dam cabin surface designing, and the method comprises the following steps: 1, three-dimensional modeling: creating a dam BIM model; 2, model sectioning: making section cutting plane according to parting and hierarchical designing of the dam and obtaining several minimum casting units and finally forming an independent shipping space; 3, additional information: adding basic information for every casting unit, including dam sections, dam chunks, elevation range, concrete intensity grade and the like; 4, cabin surface designing: selecting the shipping space used for cabin designing, taking advantages of the cabin surface characteristics included in the sipping space and then analyzing and confirming casting parameters, casting equipment, cabin entering way and the like, and finally finishing the cabin designing. Compared with the prior art, the BIM assisted dam cabin surface designing has the advantages of perceptual intuition, accuracy and high efficiency.