Finally..i have a solution for this problem..still i don't know why..after uninstall and downgrade to arcgis v.10..i can generate directions for my route..but i think this is not a good choice
After uninstall and install arcgis 10 and 10.1 several time, my conclusion "arcgis 10.1 sp 1" that made me cannot generate directions for route in my network analysis.