The invention provides a mould pressing device of a composite material. The mould pressing device of the composite material comprises an upper hot press plate, a concave mould, a convex mould and a lower hot press plate, wherein the concave mould comprises a middle sunken area and a platform area surrounding the sunken area; the convex mould comprises a middle protruded area and a platform area surrounding the protruded area; at least one exhaust slot is formed in an adjacent area of the platform area and the sunken area of the convex mould. A mould pressing method of the composite material, which is further provided by the invention, comprises a process of controlling the upper hot press plate and the lower hot press plate to tight fold the concave mould and the convex mould so as to heat and pressurize materials in a mould, wherein air in the mould is discharged through the exhaust slot in the heating and pressurizing process. According to the mould pressing device and the mould pressing method of the composite material, which are provided by the invention, the problem of air trapping in a mould pressing process can be effectively solved, and the surface effect of product shells is improved.