The invention relates to a multi-petal composite material launching box cover and a preparation method thereof and belongs to the technical field of missile launching. The multi-petal composite material launching box cover sequentially comprises a frame (1), a side sub-cover (5) and a top sub-cover (6). The side sub-cover (5) is connected with the frame (1) through a thrown body separating area (2), the top sub-cover (6) is connected with the side sub-cover (5) through a top sub-cover separating area (4), the side sub-cover (5) is evenly divided into 4-8 side sub-cover units in the circumference, and the side sub-cover units are connected through side sub-cover unit separating areas (3). Under the effect of missile launching tail flow, the launching box cover is broken into a plurality of sub-covers to fly away from a launching box, and accordingly missile launching is not influenced. The problem that a thrown object of the fragile cover is high in mass is solved, and the threat to surrounding devices and workers caused by the thrown object is effectively reduced.