The utility model relates to the field of medical instruments, in particular to an intraoral impression preparation device and assembly for a patient with maxillary defect. The device body comprises atray base and a supporting unit. A plurality of detachable supporting units are installed on the tray base, the supporting units support and improve the connecting strength between the impression material and the tray, and the supporting units in different shapes can provide comprehensive strategy support for various jaw bone defect patients. The tray base and the supporting units are used for loading impression materials, and before the impression materials are loaded, the types, the number and the installation positions of the supporting units are determined according to the shape of the defect cavity wall of the maxilla defect patient. The assembly is mainly used for magnetic connection, taking-out and resetting of the multi-layer impression. According to the device, a matrix thought is adopted, while the position and three-dimensional space information of the defect cavity are reserved, the whole jaw defect cavity record is replaced and improved into local fine adjustment, and incombination with a layering mode for complex cases, the technical difficulty of clinical operation is reduced, injuries to a patient are reduced, and the safety of impression preparation is improved.