3-D　printing　is　an　additive　manufacturing　process,　which　enables　products　to　be　custom　designed.　Obtaining　the　evolution　trend　and　identifying　the　potential　R&D　hotspots　of　3-D　printing　technology　are　important　strategic　issues　for　both　nations　and　enterprises.　In　this　article,　a　combination　method　is　proposed　using　the　Viterbi　algorithm　to　identify　technological　terms　in　patents,　using　the　latent　Dirichlet　allocation　model　to　capture　potential　technological　topics　in　patents,　and　using　the　hidden　Markov　model　to　analyze　the　distribution　and　evolution　pattern　of　the　technological　topics.　Based　on　the　results,　technological　topics　and　future　R&D　hotspots　in　3-D　printing　are　identified.　Among　the　technological　topics,　extrusion　devices　and　laser　powder　molding　are　gradually　losing　R　&　D;　model　acquisition,　extrusion　devices,　rotary　printing,　and　denture　are　the　key　topics　of　technological　evolution　that　are　difficult　to　overcome;　laser　focusing,　print　head,　color　printing,　recyclable,　feeding,　control　panel,　and　denture　will　become　the　focus　of　R&D　in　the　near　future.　Finally,　a　comparison　and　experiments　are　given　to　demonstrate　the　plausibility　of　our　method.