The invention discloses a multi-material part 3D printing device and a printing method thereof. The device is composed of a support device, a controllable stirring extrusion head device, a plurality of digital material supply systems, a work platform and a controller. Controllable stirring extrusion heads and the controller are fixedly arranged on the support device. The digital material supply systems are fixedly arranged below the multiple controllable stirring extrusion heads, and the work platform is arranged in the support device. The printing method sequentially comprises the steps of mixed slurry preparing, data modeling treatment, multi-material printing forming, removing of a macromolecule bonding agent in a blank and sintering. The feed amount of various materials is controlled through the digital material supply systems, the proportion of components of the mixed materials is controlled accordingly, the components and proportions of the materials are different according to different space positions, and after degreasing and sintering are finished, parts with the material components constantly changing according to the different positions can be obtained. The technology is simple, the cost is low, and the materials are saved.