The invention discloses a multi-material 3D printer and a liquid matter accumulation 3D printing method. A printing head switching mechanism and a printing head frame are installed on a 3D printer frame, and multiple printing heads are arranged. Different printing materials are placed in the different printing heads, and meanwhile a material afterprocessing device is installed on the printing head frame for preprocessing printed materials. By means of the technical scheme, the thermoplastic material can be firstly used for establishing a container with a complex space structure, the container is filled with liquid matter while being constructed, and therefore the space configuration of the liquid matter can be accurately controlled. By means of the multi-material 3D printer and the liquid matter accumulation 3D printing method, the single-material 3D printing technology is expanded to the multi-material 3D printing field; running of the multi-material 3D printer is reliable, and precision is high; the materials can be reprocessed while 3D printing is conducted; 3D printing of low-viscosity liquid matter can be achieved, and a good market prospect is achieved.