The amount of supporting structure usage has been a major research topic in layer-based additive manufacturing (AM) over the past years as it leads to increased fabrication time and decreased surface quality.Previous studies focused on deformation and topology optimization to eliminate the number of support structures.However,during the actual fabrication process,the properties of shape and topology are essential.Therefore,they should not be modified casually.In this study,we present an optimizer that reduces the number of supporting structures by identifying the prime printing direction.Without rotation,models are projected in each direction in space,and the basis units involved in the generation of support structures are separated.Furthermore,the area of the supporting structures is calculated.Eventually,the prime printing direction with minimal supporting area is obtained through patte-searching method.The results of the experiment demonstrated that the printing area was reduced by up to 60％ for some cases,and the surface quality was also improved correspondingly.Furthermore,both the material consumption and fabrication time were decreased in most cases.In future work,additional factors will be considered,such as the height of the supporting structures and the adhesion locations to improve the efficiency of this optimizer.