A prism apparatus and a projection device are provided. The prism apparatus includes a prism body, a first combining assembly, and a second combining assembly. The prism body includes prisms connected in sequence in a light guiding direction, and a gap is formed at a position where at least two adjacent ones of the prisms are connected to each other. The first combining assembly is arranged parallel to the light guiding direction, located at seams of the prisms, and connected to the prisms. The second combining assembly is arranged parallel to the light guiding direction, and covers and is connected to the first combining assembly.