The invention provides an assembled building deepening design method based on BII software. The assembled building deepening design method comprises the following steps of 1, conducting preliminary modeling and collision analysis; 2, conducting model deepening design; 3, automatically generating member production drawing through a model; 4, conducting engineering amount statistics and processing data management; 5, designing a mold of a prefabricated member; 6, conducting transportation vehicle-loading simulating and optimizing according to the member weight and the profile size; 7, conductingfield hoisting and simulating of the prefabricated member, and optimizing the hoisting sequence. Aiming at defects of an existing prefabricated member deepening design method, it is adopted that firstly, a three-dimensional model is modeled before deepening design drawing is drawn, a three-dimensional examination method is adopted, after the space conflict relation between the prefabricated member is excluded, the drawing is generated, a large amount of modification of the drawing is avoided, parts in the model all have the accurate three-dimensional size, material information and member subordination relationship, a member material list can be generated simply by conveying the information, and thus an accurate and efficient effect is achieved.