A production line, using a plurality of 3D printing apparatus, each of 3D printing apparatus comprising a frame assembly, and a powder spreading unit, a powder spreading movement system, a powder supply device, an inkjet unit, an inkjet movement system, a working box, a transfer unit, an inner lifting mechanism, an outer lifting mechanism, an accessory unit and an auxiliary unit that are mounted on the frame assembly comprising an upper layer frame and a lower layer frame, the powder spreading unit is connected with the lower layer frame by means of the powder spreading movement system and can move in a Y direction, the inkjet unit is connected with the upper layer frame by means of the inkjet movement system and can reciprocate in a X direction and the Y direction, the transfer unit comprises an outer roller table and an inner roller table that each comprise a driving mechanism and are configured to convey the working box, the inner roller table is provided in the lower layer frame below the powder spreading unit, the outer roller table is engaged with the inner roller table, the inner lifting mechanism is provided below the inner roller table, and the outer lifting mechanism is provided below the outer roller table, wherein a sand cleaning device is provided at a side of the outer lifting mechanism of the 3D printing apparatus, characterized in that the production line comprises an intermediate transfer device, wherein both sides of the intermediate transfer device are provided with a plurality of 3D printing apparatuses, a transition roller table is provided at a junction between the intermediate transfer device and the outer roller table of each of the plurality of 3D printing apparatuses, two ends of the intermediate transfer device in a transferring and conveying direction thereof respectively extend beyond areas of the 3D printing apparatus, with the areas arranged in a same direction, one end of the intermediate transfer device is perpendicularly provided with a collecting and distributing roller table for empty working box, the other end of the intermediate transfer device is perpendicularly provided with an intermediate roller table, a first direction-changing device and a second direction-changing device are provided at positions where the intermediate transfer device perpendicularly intersects the collecting and distributing roller table for empty working box and the intermediate roller table, respectively, the collecting and distributing roller table for empty working box extends symmetrically towards both ends and extends beyond areas of the 3D printing apparatus, with the areas arranged in the same direction and the collecting and distributing roller table for empty working box is connected with an transfer roller table for empty working box by means of a third direction-changing device, and a conveying direction of the transfer roller table for empty working box is perpendicular to a conveying direction of the collecting and distributing roller table for empty working box; a storage area is provided in an area where the intermediate roller table perpendicularly intersects a respective transfer roller table for empty working box; and baking devices are provided on both sides of each intermediate roller table, and a sand cleaning device is provided at a side of the outer lifting mechanism of the 3D printing apparatus, or further comprising an intermediate transfer device, wherein both sides of the intermediate transfer device are provided with a plurality of 3D printing apparatuses, a transition roller table is provided at a junction between the intermediate transfer device and the outer roller table of each of the 3D printing apparatuses, two ends of the intermediate transfer device in a transferring and conveying direction thereof respectively extend beyond areas of the 3D printing apparatus, with the areas arranged in a same direction, one end of the intermediate transfer device is provided with a first direction-changing device, one side of the first direction-changing device is provided with a transient storage roller table for to-be-baked working box, the other side of the first direction-changing device is provided with a transfer roller table and a collecting and distributing roller table for empty working box that are arranged in parallel, the other end of the transfer roller table and the collecting and distributing roller table for empty working box is provided with a storage area, and the outer side of the first direction-changing device relative to the intermediate transfer device is provided with a baking device.