With helical gears as the casting test object, the moldless rapid precision casting technology of plaster mold was studied by four stages as casting mold design, 3D printing, dewatering and casting parts along the process flow. The results show that when the shape of the casting parts is complex, the partition structure is more advantageous to the cleaning of the cavity interior than the whole casting; the surface of the cavity inside the plaster casting does not need to be brushed with silica sol or sodium silicate, but needs to be dewatered, otherwise the casting is prone to defects such as blowhole; the filling capacity of plaster mold is better than that of the sand mold. The plaster mold is easy to clean. The dimensional precision of the part casted can reach CT5 ~ CT6, and the Ra value of surface roughness can reach 3.2 ~ 6.3 μm.