can i take mrt from nanjing road to shanghai airport? how long the travel time?

If you refer to Pudong Airport, yes, you can. Take subway line 1 at East Nanjing Road metro station to get there directly! It takes around an hour and the metro fee is CNY7 per person.

But the Maglev connects Longyang Road and Puodng Airport, so you cannot catch that at Nanjing Road. If you wish to experience that, take metro line 2 from East Nanjing Road to Longyang Road and then transfer to the Maglev to get to the airport in 8min.