Abstract: The time of film-covering was studied, the results showed that removing film in middle growth period was conducive to the growth of tobacco plant roots. If film was removed in 30 days after transplanting, the dry weight of root was 1.72 times as that of root covered by film in whole growth period. The nitrogen, potassium, magnesium and boron moved up and rich in the top of ridge with film-covering. The contents of alkaloid nitrogen, soluble boron, rapidly available potassium, and exchangeable magnesium in the top layer of ridge (1.5cm below surface) at the end of growth period were 937.58mg/kg, 1.60mg/kg, 2136.06mg/kg, and 143.96mg/kg, respectively. The nicotine contents in upper leaves were higher with removing film in middle growth period.