Go to Xinzhuang first, walk from Xinzhuang subway station along Shen Jian East Road to Qixin Road, turn right (10 minute walk), get on Shenlong Line (Shen Jian East Road Station) and get off at (Shanghai Botanical Garden Station), walk south along Longwu Road 10 minute, and the entrance of Shanghai Botanical Garden Station is not far from the bridge.
Including the walking time, it is about 1 hour.