The invention discloses a combined-type ceiling suspension device under a high-large curved surface steel structure and a mounting method thereof. The combined-type ceiling suspension device comprisesa tray, a hanging disk, adjustable multi-directional outward-extending arms and adjustable connecting units. The tray is connected with a connecting steel structure main body part and a main hangingrod. The main hanging rod is connected with the tray and the hanging disk. The adjustable multi-directional outward-extending arms are connected with the hanging disk and the adjustable connecting units. Auxiliary hanging rods are connected with the adjustable multi-directional outward-extending arms and adjustable hanging pieces. U-shaped clamping grooves are formed in the adjustable connecting units. According to the combined-type ceiling suspension device, materials can be saved, decorative face plates are in streamlined transition in the space, and extremely-high adaptability to the structures of the decorative face plates with the complex shapes is achieved; and according to the mounting method, positioning is accurate, the shape is attractive, quick assembling can be conducted, the construction period is shortened, and the construction efficiency is greatly improved while the overall facing quality of a curved surface ceiling is met.