Microsphere-assisted　optical　microscopy　achieved　the　nano-scale　resolution　for　the　imaging.　Some　parts　of　evanescent　waves　produced　by　nano-structures　can　be　transformed　into　propagating　waves　with　the　help　of　microsphere.　In　this　paper,　we　develop　the　equations　of　the　resolution　and　field　of　view　in　microsphere　imaging　system　related　to　the　radius　and　refractive　index　of　microsphere.　Through　analysis　the　highest　spatial　frequency,　the　resolution　reduces　quickly　with　the　increase　of　the　radius　when　the　radius　is　less　than　10　mu　m.　The　resolution　reduces　slowly　with　the　increase　of　the　radius　when　the　radius　is　more　than　10　mu　m.　The　resolution　improves　with　the　increase　of　refractive　index.　The　size　of　the　focus　spot　of　microsphere　is　simulated　numerically.　The　simulations　are　in　good　agreement　with　the　theoretical　prediction　about　the　microsphere-assisted　microscopy.　Finally,　the　super-resolution　capability　of　the　microsphere　has　been　verified　by　the　experimental　results.　The　results　are　useful　for　the　practical　design　of　the　microsphere-assisted　optical　microscopy.