Take a bus from Wuxi to Suzhou North Bus Station, then take the No.5 tour to Suda North Campus/xiangmen and get off at 178 and get off at Xi 'an Jiaotong University.
This is basically the route. If it's your first visit to Suzhou, you'd better get off at Suzhou Bus Station and buy a map with bus lines on it, which is convenient and not easy to go wrong.