Abstract: Six conventional water chemistry parameters of petroleum contaminated groundwater were monitored by on-situ water quality monitor apparatus． The study illustrated the effects of measuring modes and measuring depths on conventional water chemistry parameters． Ｒesults indicated that at 0. 5m below the petroleum contaminated groundwater，the temperature，pH， dissolved oxygen，redox potential and turbidity varied under the condition of on-situ and ex-situ measurement． In the comparative study period，differences could be observed up to: Temperature of 5 ～ 6 ℃，pH of 0. 2，DO of 3. 0 mg /L，redox potential of 11 mV，turbidity of 55 NTU． The change of groundwater environmental condition would inevitably lead to a series of hydrogeochemical and biogeochemical reactions changes． Within the depth of 0. 5 ～ 4 m under the condition of on-situ measurement，temperature went up with depth increasing，and the maximum amplitude was 0. 16 ℃; pH changed little with increasing depth of groundwater; DO decreased with increasing depth affected by temperature and biochemical oxygen consumption; OＲP and DO had the same trends，and the maximum reduction of OＲP was 62 mV; conductivity unchanged with increasing depth of groundwater; the maximum turbidity of 113 NTU appeared at a depth of 4 m．