Digital　holographic　microscopy　has　been　widely　used　for　the　imaging　of　micro-objects　and　biological　samples.　Lensless　in-line　digital　holographic　microscopy　is　capable　of　wide　field-of-view　imaging.　However　the　spatial　resolution　of　the　reconstructed　images　is　limited　by　the　pixel　size　of　the　detector.　The　relative　position　shift　between　the　sample　and　the　detector　can　effectively　improve　the　resolution　in　the　traditional　sub-pixel　shifting　method,　but　it　requires　a　high　precision　of　translation　stage.　To　overcome　this　problem,　we　propose　a　method　based　on　the　point　source　scanning　to　realize　sub-pixel　shifting.　High　precision　sub-pixel　shifting　is　achieved　easily　by　using　the　geometric　between　point　source　and　detector.　Through　moving　the　point　source,　multiple　holograms　with　sub-pixel　shifts　are　captured.　These　holograms　are　merged　together　to　obtained　a　high　resolution　hologram　by　a　synthesizing　algorithm.　Then,　the　high　resolution　reconstructed　image　of　the　object　can　be　obtained　by　the　angular　spectrum　algorithm.　The　feasibility　of　the　proposed　method　is　demonstrated　by　simulation　and　experiments.　A　USAF　resolution　test　target　was　used　as　the　object.　Compared　with　the　traditional　digital　holography,　a　higher　resolution　reconstructed　image　is　obtained　by　our　method.　The　proposed　method　has　the　advantages　of　simple　recording　setup　and　lower　precision　requirement　of　the　translation　stage.　It　can　achieve　the　wide　field-of-view　and　high　resolution　imaging.