Digital　holography　combines　the　advantages　of　the　optical　holography　and　the　computers.　It　can　implement　an　all-digital　processing　and　has　the　quasi　real-time　property.　With　lensless　Fourier　transform　recording　architecture,　the　limited　bandwidth　of　CCD　camera　can　be　utilized　sufficiently,　and　the　sampling　theorem　is　satisfied　easily.　Therefore,　high-resolution　can　be　achieved.　So　it　is　preferred　in　the　microstructure　imaging.　In　the　paper,　based　on　the　Fresnel　diffraction　theory　and　the　off-axis　lensless　Fourier　transform　recording　architecture,　the　experimental　optimization　and　correspondingly　the　digital　reconstruction　was　investigated.　Also,　the　lateral　resolution　of　the　reconstructed　image　was　analyzed　and　improved　by　the　proposed　techniques.　When　the　USAF　test　target　was　imaged　without　any　pre-magnification,　the　lateral　resolution　of　3.1　mu　m　was　achieved,　which　matched　the　theoretical　prediction　very　well.　The　key　points　to　achieve　high　resolution　image　are　to　use　the　smaller　object　and　to　arrange　the　distance　between　the　object　and　the　CCD　plane　as　short　as　possible.　Meanwhile,　properly　overlapping　the　reconstructed　image　with　the　DC　term　was　helpful　to　improve　the　resolution.　The　noise　in　the　reconstructed　image　could　be　reduced　greatly　by　choosing　the　optical　elements　precisely　and　adjusting　the　beam　path　finely.　The　experimental　results　demonstrated　that　it　is　possible　for　the　digital　holographic　microscopy　to　produce　the　high　resolution　image　without　the　objective　pre-magnification.　The　results　also　showed　that,　with　a　high　quality　hologram,　the　special　image　processing　during　the　reconstruction　may　be　unnecessary　to　obtain　a　high　quality　image.