Amberlite XAD-7 resin was modified by room temprature ionic liquid (1-hexyl-3-methylimidazolium hexafluorophosphate, ［C6mim］PF6) coating through a maceration method, gaining a new sort of hydrophobic adsorbent for the solid phase extraction mini-column. Trace inorganic mercury in wastewater samples was preconcentrated and determined by flow injection on-line mini-column sampling coupled with spectrophotometric determination. In acid medium, dithizone was employed as chelator with cetyltrimethylammonium bromide (CTMAB) to form a red neutral mercury-dithizone complex, which could be extracted quantificationally by solid phase extraction technique on the mini-column.Under the optimized conditions, the linearity and the detection limit of the proposed method were found to be 0.35 to 50.0 μg·L-1 Hg2+ and 0.067 μg·L-1 Hg2+, respectively. The enrichment factor of 25 times could be achieved with a 50 mL sampling volume and the developed procedure was successfully applied for the determination of mercury in the certified reference material (GSBZ50016-90) and the spiked dock wastewater samples with the recovery of 99%-103%.