to romullus:i tried to save the map into a 8bit format and also using the coronabitmap node but it seems not gonnan work properly as well. and i tried to use the same displacement map but using vray engine and it could be already rendered correctly so i think the problem may be not about the too narrow dynamic range.
accidentally i solved this problem by creating a completely new polysurface and roughly made it like the geometry before. now corona could rendern it very well to some how. I am not quite sure about the logic behind this. But for a better unterstanding:the whole oringinal geometry (about 5km with around 600k polys) was exported from a GIS software and edited in Rhino. after imported into 3dsmax i selected an area (600m x 1000m) and detached it as a new object. after applying the material i mentioned before and also the displacementmod the problem with those stripe effects come up. dont know if there is something wrong during these processes but it seems to be the problem of the geometry.