Franckeite(Pb5Sn3;Sb2S14)is a kind of complex layered sulfide. The structure can be viewed as an alternate stacking of two false tetragonal symmetric t sheets(galena PbS sheets) and one false hexagonal symmetric h sheet(berndtite SnS2 sheet)along[100].Two kinds of sheets are packed in order of htthtt……along a axis. Because the unit cell of t sheets cannot correspond with the unit cell of h sheet and the missed matching between t sheets and h sheets the incommensurate-sinusoidal modulation waves have formed along c axis. Using type CSTMM一9000 Scanning Tunneling Microscopy, the authors observed the cleavage face {100}of franckeite and obtained excellent distinct atomic resolution STM image.The lattice parameters AB=0.366nm, AD=0.620nm indicated h sheet atomic arrangement of the cleavage face. The modulation sinusoidal waves of 4.7nm along caxis and a superstructure long period of 6. 98nm along b axis were also observed.Meanwhile the microtopographic character of franckeite was investigated with STM.