The utility model relates to an ink jet printer unites conveying system for building materials, the ink jet printer who meets around at least two, every ink jet printer possesses respective belt transport system, its characterized in that: the solitary belt transfer system of another cover has been add on two end to end's the ink jet printer, this solitary belt transfer system strides on the ink jet printer's who meets around in conveyor belt, such design, can reduce the belt of third cover system and the frictional force and the tension of ink jet printer platform, like this can the effectual life who prolongs principal and subordinate's action roller, increase the counterpoint precision, and the qualification rate of the products can be improved, use when more can realize A variety of colors ink and multiple functions ink, the fancy variety of effectual increase adobe, improve the competitive power of product.