In　this　article,　we　investigate　the　problems　existing　in　the　lithography　on　the　deep　multi-stepped　surface.　Different　photoresist　thicknesses　above　and　under　the　step　are　measured　in　experiment.　The　relationship　between　step　height　and　photoresist　thickness　is　discussed　and　numerically　described.　Based　on　the　description　of　Beer　model　about　the　light　absorption　coefficient,　the　curves　of　different　light　transmittances　at　different　times　are　analysed.　Reasons　why　the　light　transmittance　changes　with　time　are　explained,　and　the　light　absorption　coefficient　is　believed　to　be　related　to　photoresist　thickness.　On　this　basis,　the　lithography　process　is　optimized.　The　patterns　with　narrow　line-width　under　the　deep　step　on　the　wafer　are　obtained.