The invention discloses an instrument for quantitatively analyzing trace oxide in petroleum hydrocarbon and a method for quantitatively analyzing the trace oxide in the petroleum hydrocarbon. The instrument comprises a sample feeding hole, two hydrogen flame ionization detectors, a damping column, a polar chromatographic column, a non-polar chromatographic column, three three-way valves, an electromagnetic switching valve and a pressure controller, wherein the sample feeding hole is connected with the non-polar chromatographic column and then is connected with the three-way valve C; the hydrogen flame ionization detector A is connected with the damping column and then is connected with the three-way valve A; the hydrogen flame ionization detector B is connected with the polar chromatographic column and then is connected with the three-way valve B; the three-way valve C is connected with the three-way valve A and the three-way valve B respectively; the three-way valve A and the three-way valve B are connected with the electromagnetic switching valve respectively; and the electromagnetic switching valve is connected with the pressure controller. According to the instrument, a novel flow path switching manner without a dead volume is adopted, a cutting range is narrow, and the detection problem of the content of the trace oxide in the petroleum hydrocarbon is solved very well; and the detection precision is high, the accurately is good, and the instrument and the method can be used for detecting the trace oxide in the petroleum hydrocarbon.