Three dimensional （3D） printing， an emerging technology， may have significant impact on the current copyright system， especially in the type of works， the concept of reproduction and the judgment criteria of fair use， etc. This paper studies the problems about the nature and reproduction of 3D printing works from microcosmic to macrocosmic perspectives by means of comparative research， empirical research， and literature research. According to the technical principle of 3D printing， it can be divided into input link and output link. The input link contains modeling by CAD software and compiling into the executable printing files for STL format. In the output link， the paper considers the process of the production of printing device outputs on the basis of the section information of STL files. And exactly， the CAD file is crucial to the connecting bearing of the input link and output link． In the part of ″input″， according to the modeling methods， the generation ways of CAD files can be classified into ″independent design modeling of CAD″ ″CAD modeling by drawings″ and ″modeling by scanning.″ Therein， only the first generation way is the original acquisition， its CAD files meet the elements of objectivity， replicability and originality， and it also possesses the possibility of copyrightability. Copyrightability is restricted to any digital model that only exists on account of its practical function without constituting a work． The opinions of academic circles on the type of works of CAD files are mainly concentrated on the computer software， graphic work fine art and model work， etc. The premise to distinguish the graphic work from the model work is to define ″three dimensions （3D）.″ The authors adopt visual criteria， i.e.， ″3D″ design can not only reflect a single perspective， but also have the ″rotatable″ function. It is an innovation point in the paper， and pushes the behavior of ″printing CAD files to material object″ to uncontroversial ″reproduction from 3D to 3D″ under the condition that the foreign copy has not been expressly stipulated. Therefore， the showing digital model of CAD file is more approximate to model work， rather than being considered as graphic work. However， there is a self-contradiction in the legal definition of model work. Fortunately， the legislature has noticed the problem and has revised to ″3D works″ in The Copyright Law Amendment Draft （Draft for Approval）. Under the current copyright law system， people can temporarily take the idea of ″fine art+model work″ to regulate CAD files and their printout material objects.  According to the above analyses from microcosmic perspective， CAD files and their printout objects can be quickly spread under the support of technology development. In the network environment， the uploaded CAD files from users， the downloading or printing others’ digital model without permission may constitute infringements. The utilization of the technological measures can help control the illegal spread of the works and greatly reduce copyright infringement disputes. In the private copying problems of printout material objects， 3D printing technology will produce a great deal of decentralized private copying， and its accumulation inevitably involves the copyright owners who originally enjoy the monopoly interest. Therefore， the authors hold that people can adopt ″three-step test″ and take example by the four factors considered in ″rationality judgment standard″ of the United States to understand ″unreasonably prejudice″， i.e.， the purpose and character of the use， nature of the work， the proportional amount and substance of the use ， and the effect on the original author’s economic market．