The present invention provides a method of manufacturing a three-dimensional product having uniform mechanical properties using an SLS 3D printer including the steps of: preparing a mixed powder material by mixing resin powder and glass bubbles, wherein the specific gravity of the glass bubbles is from about 0.8 to about 1.2 times that of the resin powder; supplying the mixed powder material to the 3D printer using a roller; and selectively sintering the mixed powder material by irradiating the powder material using a laser based on 3D data of the product to be manufactured.